Commercial_Poultry_Nutrition

244 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.14 Vitamin-Mineral Premixes (starter or general) Vitamin A (I.U) Hubbard Ross Cobb Vitamin D3 (I.U) Vitamin E (I.U) 7000 8270 12000 Vitamin K3 (I.U) 3500 3030 4000 Thiamin (mg) 40 50 30 Riboflavin (mg) 2.2 2.2 4.0 Pantothenate acid (mg) 4.0 2.4 4.0 Niacin (mg) 6.0 7.7 9.0 Pyridoxine (mg) 11.0 12.7 Choline (mg) 51.8 4.0 Folic acid (mg) 45 2.4 400 Biotin (µg) 3.3 1.5 Vitamin B12 (µg) 750 - 150 1.0 1.1 20 Manganese (mg) 100 110 Zinc (mg) 12 15.4 120 Iron (mg) 100 Copper (mg) 66 120 40 Iodine (mg) 50 110 20 Selenium (mg) 80 20 1.0 9.0 16 0.30 1.0 1.25 0.30 0.30 b) Prestarters The role of the unabsorbed yolk sac in early life nutrition is open to debate. On an evolutionary It is generally recognized that the neonate chick scale the yolk sac likely provides a source of ener- does not produce an adult complex of digestive gy, water and perhaps, most importantly, IgA enzymes, and so digestibility is somewhat maternal antibodies for the young bird. Most altri- impaired. This situation is further complicated cial birds have virtually no yolk sac, while pre- by the change in nutrient substrate of lipid and cocial birds have considerable yolk reserves at protein in the embryo to quite complex carbo- hatch. The yolk sac in chicks weighs around 8- hydrates, proteins and lipids in conventional starter 10 g depending on the size of the original egg diets. So even though chicks grow quite rapid- yolk. It is often stated that the residual yolk will ly in the first few days of life, there is the idea that be used more quickly if the chick is without feed this could be further enhanced by use of a and water. It seems that yolk utilization is unaf- prestarter. Prestarters therefore, either pre-con- fected by presence or not of feed with a linear dition the chick such that it can digest complex decline in yolk weight up to 3 d post-hatch. By substrates and/or provide more (or more high- day 3, regardless of feed supply, yolk size is only ly digestible) substrates until the chick’s enzyme around 2-3 g. During this time there is an production has ‘matured’. SECTION 5.2 Feeding programs

CHAPTER 5 245 FEEDING PROGRAMS FOR BROILER CHICKENS increase in enzyme supply within the intestin- The idea in formulating prestarter diets is to al lumen. Specific activity of individual enzymes correct any such deficiency, and so hopefully actually declines over the first week of life, increase early growth rate and/or improve uni- although this is compensated for by rapid formity of such early growth. Two types of increase in secretory cell numbers. Early cell dam- prestarter diets are used for broiler chickens. The age, especially in the duodenum will greatly first option is to use greater than normal levels impair digestion. of nutrients while the alternate approach is to use more highly digestible ingredients. According While corn-soybean meal diets are regard- to Figure 5.1, if we increase nutrient supply by ed as ideal for poultry, there is evidence that 10-15%, it should be possible to correct any defi- digestibility is sub-optimal for the young chick. ciency in digestibility, and so realize expected Parsons and co-workers show reduced AMEn and AMEn and amino acid utilization. A potential amino acid digestion in chicks less than 7-10 d problem with this approach is the acceptance that of age (Figure 5.1). nutrients will not be optimally digested and that such undigested nutrients will fuel micro- Figure 5.1 Age effect on AMEn and lysine bial overgrowth. digestion of a corn-soy diet (Batal and Parsons, 2002) An alternate approach is to use more high- ly digestible ingredients, with little change in level With some 10% reduction in nutrient diges- of nutrients. Such prestarter diets are going to tion compared to expected values, it is obvious be very expensive, since alternative ingredi- that our conventional starter diets are not ideal ents are invariably more expensive than are for young chicks. corn and soybean meal. Table 5.15 shows ingredients that could be considered in formu- lating specialized prestarter diets. Using these ingredients, it is possible to achieve 190-200 g body weight at 7 d, compared to 150-160 g with conventional corn-soybean diets. This improved early growth rate contin- ues during most of the subsequent grow-out period (Table 5.16). In this study, male broilers were 34% heav- ier than standard, when a highly digestible prestarter was fed for the first 4 d. Because of the ingredients used in formulation, this prestarter was twice as expensive as the conventional corn-soy starter diet. As shown in Table 5.16, the advantage of using the prestarter diminishes with age, although birds were still significantly heavier at 42 d. Interestingly, the highly digestible prestarter had no effect on uniformity of body SECTION 5.2 Feeding programs

246 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.15 Potential ingredients for highly digestible prestarter diets Cereals Rice Max. Corn % inclusion Glucose (cerelose) Oat groats 40 30 5 5 Proteins Fish meal 5 Fish protein concentrate 5 Blood plasma 10 Casein 8 Soybean meal 20 Alfalfa 4 Fats Vegetable oil 4 Additives Wheat enzyme Mannanoligosaccharide Probiotic Lactic acid Table 5.16 Effect of using a highly digestible prestarter to 4 d of age, on growth of male broilers Age (days) 4d 7 d 21 d 33d 42d 2670 Prestarter (0-4 d) 117 190 820 1900 2450 Conventional 9% Difference 87 150 700 1700 34% 21% 17% 12% (Swidersky 2002, unpublished data) weight at any time during the trial. In this and it is obvious that the birds will necessarily con- other studies, we have seen no advantage to using sume more of these diets and that birds may also so called ‘mini-pellets’ vs. using good quality take longer to reach market weight. These two fine crumbles. factors result in reduced feed efficiency. Surprisingly, broiler chickens seem to perform quite c) Low nutrient dense diets reasonably with low nutrient dense diets, and in certain situations these may prove to be the By offering low protein, low energy diets (Table most economical program. If diets of low 5.2) it is hoped to reduce feed costs. However, SECTION 5.2 Feeding programs

CHAPTER 5 247 FEEDING PROGRAMS FOR BROILER CHICKENS energy level are fed, the broiler will eat more feed energy intake is rarely achieved and this fact is (Table 5.17). the basis for programs aimed at reducing early growth rate. However, live body weight is often In this study, only the energy level was not the ‘end-point’ of consideration for broiler changed and the broiler adjusted reasonably well production, since carcass weight and carcass com- in an attempt to maintain constant energy intake. position are often important. From the point of Diet energy from 3300 – 2700 kcal ME/kg had view of the processor or integrator, these cheap- no significant effect on body weight, and this sug- er diets may be less attractive. Carcass weight gests the bird is still eating for its energy need. and meat yield are often reduced, and this is asso- Obviously these data on growth rate are con- ciated with increased deposition of carcass fat, founded with the intake of all nutrients other than especially in the abdominal region. Low protein energy. For example, birds offered the diet diets are therefore less attractive when one con- with 2700 kcal ME/kg increased their protein intake siders feed cost/kg edible carcass or feed cost/kg in an attempt to meet energy needs. Using edible meat. This consideration of carcass com- these same diets, but controlling feed intake at position leads to development of diets that max- a constant level for all birds (Table 5.18) shows imize lean meat yield. that energy intake per se is a critical factor in affect- ing growth rate. Another concept for feeding broilers is true low nutrient dense diets, where all nutrient con- With low energy diets, therefore, we can expect centrations are reduced (in practice energy and slightly reduced growth rate because ‘normal’ protein/amino acids are most often the only Table 5.17 Performance of broilers fed diets of variable energy content Diet ME Body weight (g) Feed intake (g/bird) (kcal/kg) 25 d 49 d 0 – 25 d 25 – 49 d 0 – 49 d 3300 1025 2812 1468 3003 4471 3100 1039 2780 1481 3620 5101 2900 977 2740 1497 3709 5206 2700 989 2752 1658 3927 5586 SECTION 5.2 Feeding programs

248 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.18 Performance of broilers given fixed quantities of feed Body weight (g) Feed intake: body weight gain Diet ME 25 d 49 d 0 – 49 d (kcal/kg) 825a 2558ab 1.84c 3300 818a 2599a 1.82c 3100 790b 2439b 1.94b 2900 764b 2303c 2.05a 2700 Table 5.19 Response of male broiler to low nutrient dense finisher diets (35 – 49 d) Diet nutrients Body wt. (g) Feed intake (g) Carcass wt. (g) Breast wt. (g) 42 d 49 d 35 – 49 d 49 d 49 d ME CP (kcal/kg) (%) 2420 2948 2583 2184 418 2367 2921 2763 2107 404 3210 18.0 2320 2879 2904 2063 400 2890 16.2 2263 2913 3272 2088 402 2570 14.4 2170 2913 3673 2073 390 2250 12.6 2218 2892 4295 2038 378 1925 10.8 1605 9.0 nutrients changed in such a program). Examples to feed intake. With the lowest nutrient dense of such diets are shown in Table 5.2. With this diet for example, which is at 50% of the control type of feeding program, one can expect slow- level of nutrients, broilers exactly doubled their er growth and inferior feed efficiency, although feed intake. The reduction in carcass and breast this should not be associated with increased fat weight is likely a reflection of reduced intake dur- deposition. Depending upon local economic con- ing the 35-42 d period of adjustment. It is not ditions and the price of corn and fat, this type of likely that 50% diet dilution is economical, yet program can be economical. the data in Table 5.19 indicates that the broiler is not eating to physical capacity, and given The older the broiler chicken, the greater its sufficient time for adjustment, can at least dou- ability to adapt to very low nutrient dense diets. ble its feed intake. In the 42-49 d period, broil- When broilers are offered very low nutrient ers fed the diet of lowest nutrient density con- dense diets in the finisher period, they adapt quite sumed over 300 g feed each day. well and growth rate is little affected (Table 5.19). In the 42-49 d period broilers adjusted d) Growth restriction almost perfectly to the low nutrient dense diets, and growth rate was maintained by adjustment Broilers are usually given unlimited access to high nutrient dense diets, or have SECTION 5.2 Feeding programs

CHAPTER 5 249 FEEDING PROGRAMS FOR BROILER CHICKENS limited access during brief periods of darkness. ier at 7 d compared to hatch weight, while 20 It is generally assumed that the faster the growth years ago. This value was closest to 200%. rate, the better the utilization of feed, since maintenance nutrient needs are minimized However, fast initial growth rate can lead to man- agement problems, such as increased incidence of Figures 5.2 and 5.3 indicate the increase in metabolic disorders. Also, if early growth rate can genetic potential of the male broiler over the last be tempered without loss in weight-for-age at 42 – 30 years. It is obvious that there has been 56 d, then there should be potential for improved major emphasis placed on early growth rate, since feed efficiency due to reduced maintenance needs. the modern broiler is now at least 300% heav- This concept is often termed compensatory gain. Figure 5.2 Male Broiler Growth over the last 30 Years Figure 5.3 Percentage weekly increase in growth of male broilers. SECTION 5.2 Feeding programs

250 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS If growth rate is to be reduced, then based Figure 5.4 Compensatory growth curve on needs to optimize feed usage, nutrient restric- exhibited by female broilers. tion must occur early in the grow out period (Table 5.20). As the bird gets older, a greater propor- benefits of improved feed efficiency are not tion of nutrients are used for maintenance and realized. This situation often happens when the less is used for growth. Therefore, reducing period of undernutrition is too prolonged, or the nutrient intake in, say the first 7 d, will have lit- degree of undernutrition is too severe. A peri- tle effect on feed efficiency, because so little feed od of undernutrition can be achieved by phys- is going towards maintenance (Table 5.20). At ical feed restriction, diet dilution or by limiting 8 weeks of age, a feed restriction program access time to feed as occurs with some light- would be more costly, because with say a 20% ing programs (see section 5.5). restriction there would likely be no growth, because 80% of nutrients must go towards In early studies, we fed broiler chickens maintenance. Early feed restriction programs there- conventional starter diets to 4 days of age and fore make sense from an energetic efficiency point then the same diet diluted with up to 55% rice of view, and are the most advantageous in pro- hulls from 6 – 11 days. After this time, the grams aimed at reducing the incidence of meta- conventional starter was reintroduced, followed bolic disorders. by regular grower and finisher diets. Table 5.21 indicates the amazing ability of the broiler Table 5.20. Proportion of energy for chicken to compensate for this drastic reduction growth vs. maintenance in nutrient intake from 6 – 11 days of age. Week (%) Distribution When broilers are fed limited quantities of Maintenance Growth feed through to market age, there is a pre- 1 dictable reduction in growth rate (Table 5.22). 2 20 80 3 30 70 When there is continuous feed restriction, feed 4 40 60 efficiency is compromised, since there is no 5 50 50 potential for compensatory growth. When feed 6 60 40 restriction is applied only during early growth, 7 70 30 then there is potential for compensatory growth 8 75 25 (Table 5.23). 80 20 If birds grow more slowly in the first few weeks and achieve normal market weight for age, then the difference in the growth curves should be proportional to the reduction in mainte- nance energy needs. Figure 5.4 shows an exam- ple of compensatory growth in female broilers, achieved by feed restriction from 4 – 10 d of age. If regular market weight-for-age is not achieved due to early life undernutrition, then SECTION 5.2 Feeding programs

CHAPTER 5 251 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.21 Effect of diet dilution with rice hulls from 6 – 11 days of age, on compensatory growth of male broiler chickens Treatment Body weight (g) Feed:gain ME/kg gain 21 d 35 d 42 d 49 d 21 – 35 d 0 – 49 d 0 – 49 d Control 50% dilution 6-11 d 733 1790 2390 2890 1.84 2.01 6.21 677 1790 2380 2950 1.70 1.93 5.90 Adapted from Zubair and Leeson (1994) Table 5.22 Effect of 5 – 15% feed restriction from 1 – 42 d on broiler growth Feeding system Body wt. (g) F:G Mortality (%) Carcass wt. (g) 2401a 5.6b 1849a Ad lib 2201b 1.68 4.5ab 1716b 5% restriction 2063bc 1.76 3.2ab 1625bc 10% restriction 1997c 1.75 1.1b 1518c 15% restriction 1.78 Adapted from Urdaneta and Leeson (2002) Table 5.23 Effect of feeding at 90% of ad-lib intake for various times, on growth and mortality of male broilers Body wt. (g) F:G Mortality (%) 35 d 49 d (0 – 49 d) Total SDS Ascites Ad-lib 1744 2967 1.75 11.7 8.3 1.7 5 – 10 d1 1696 2931 1.71 5 – 15 d 1725 2934 1.69 8.3 4.9 1.7 5 – 20 d 1727 2959 1.70 5 – 25 d 1734 2947 1.69 8.3 3.3 1.7 5 – 30 d 1676 2875 1.69 8.3 4.9 1.7 8.3 4.9 1.7 5.1 1.6 0 With 10% feed restriction from 5 up to 25 days 190% of ad-lib of age, there was minimal effect on growth rate, although feed efficiency was improved. This able. The early work of Plavnik and co-workers improvement in feed utilization is a conse- suggested that feeding to maintenance energy quence of reduced mortality and reduced main- needs from 4 – 11 d of age resulted in a marked tenance need due to slower initial growth. reduction in carcass fatness and especially yield When feed restriction occurs in the mid-period of the abdominal fat pad. The reasoning behind of growth (14 – 28 d) there is little effect on mor- reduced fatness was limited early growth of tality and growth compensation is rarely achieved. adipose cells. We have not been able to con- sistently duplicate these results. However, in most The results of early feed restriction or under- studies, even when body weight compensation nutrition on carcass composition are quite vari- is achieved, there are often subtle reductions in carcass yield and especially breast meat yield. SECTION 5.2 Feeding programs

252 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS A consistent result of early undernutrition is severe restriction programs for male broilers. Feed reduction in the incidence of metabolic disor- restriction can start as early as 3 – 4 d. Table 5.24 ders and especially SDS. Although such conditions shows cumulative feed intake expected in the first are less problematic than 5 –10 years ago they week together with subsequent intakes each 2 often still represent the major cause of mortal- d. The cumulative intake data takes into account ity and condemnations, and any reduction in mor- the intake on the odd days not shown. tality is of economic importance. It seems as though early undernutrition can be economical e) Heavy broilers/roasters as long as final weight-for-age is not compromised. In relation to its mature weight, the broiler A practical problem with diet dilution or feed chicken is marketed at a relatively young age. At restriction, is deciding on levels of anticoccidi- 49 – 56 d, growth rate of the male bird is still lin- als and other feed additives. With diet dilution, ear, even though maximum growth rate occurs birds will eat much more feed. If for example, at 5 – 6 weeks of age. Modern strains of male feed intake is doubled due to a 50% dilution, broilers are still able to increase their body should the level of anticoccidial be reduced weight by 450-500 g each week through to 11 by 50%? With 50% feed restriction on the or 12 weeks of age. The breast yield of these older other hand, does there need to be an increase birds is maintained, and so very heavy broilers in concentration of these additives? This general or roasters find ready niche markets. The major area needs careful consideration, and results may challenge in growing these heavy birds is pre- well vary with the chemical compounds under venting high levels of mortality. In a recent consideration due to potential toxicity at criti- study in which broilers were offered ad-lib feed cal levels. to a mature weight of around 8 kg, 70% mortality occurred in the male birds. Where broilers are necessarily grown at high altitude or when birds are exposed to envi- Perhaps the most important consideration in ronmental temperatures of <15˚C, mortality growing heavy broilers is development of spe- due to ascites is inevitable. Although the breed- cialized feed programs that are not merely ‘con- ing companies have selected against this condition, tinuations’ of conventional 0 - 49 d broiler pro- mortality of up to 10% is still common in male grams. Table 5.3 provides examples of diets for broilers grown under these adverse conditions. heavy broilers grown to 60 – 70 d of age. There In these situations, mild feed restriction through- seems to be no need for high nutrient dense diets out rearing is often economical, where the 2 – at any time during growout, and even single stage 3 d longer growing period is offset by much lower low-nutrient dense diets give reasonable results mortality. Table 5.24 gives examples of mild and (Table 5.25). SECTION 5.2 Feeding programs

Age (d) Standard Program (g/b) Severe Restriction (g/b) Mild Restriction (g/b) Table 5.24 Examples of mild and severe feed restriction programs aimed at CHAPTER 5 Daily Cumulative Daily Cumulative Daily Cumulative reducing incidence of metabolic disorders FEEDING PROGRAMS FOR BROILER CHICKENS 8 10 34 184 31 171 32 174 12 49 274 44 252 46 258 14 58 387 49 351 55 365 16 72 524 61 467 66 491 18 81 680 69 600 75 636 20 91 857 77 750 85 801 22 100 1053 85 917 96 988 24 109 1266 98 1108 105 1193 26 118 1497 106 1316 115 1416 28 124 1743 112 1538 122 1658 30 132 2003 123 1776 130 1913 32 139 2277 129 2030 139 2187 34 147 2566 137 2299 147 2476 36 154 2871 146 2586 154 2781 38 159 3188 151 2887 159 3098 40 163 3512 155 3195 163 3422 42 167 3844 159 3510 167 3754 44 171 4184 162 3833 171 4094 46 173 4529 164 4161 173 4439 176 4880 167 4494 176 4790 48 180 5237 176 4844 180 5147 SECTION 5.2 Feeding programs 253

254 SECTION 5.2 Table 5.25 Growth of male broilers to 70 d when fed diets of varying CHAPTER 5 Feeding programs nutrient density FEEDING PROGRAMS FOR BROILER CHICKENS Diet CP:ME (%:kcal/kg) Body wt F:G Mortality Protein Energy Relative feed (g) (%) efficiency efficiency cost 0-21 d 21 – 49 d 49 – 70 d 0 – 70 d 20:3100 18:3100 16:3200 70 d 2.26b 0 – 70 d kg/kg gain Mcal/kg gain (per kg gain) 20:3100 18:2900 16:2800 4193a 2.55a 19.2 0.39c 7.1ab 100 20:3100 18:2900 18:2900 4088ab 2.48a 16.7 0.44b 7.3ab 101 20:3100 20:3100 20:3100 4077ab 2.40ab 16.7 0.45ab 7.2ab 97 18:2900 18:2900 18:2900 4046ab 2.45ab 12.5 0.48a 7.4a 105 16:2800 16:2800 16:2800 4260a 2.45ab 13.3 0.39c 6.9b 85 3753b 10.8 0.39c 6.9b 85 Leeson et al. 2000

CHAPTER 5 255 FEEDING PROGRAMS FOR BROILER CHICKENS Only with the single diet of 16% CP at 2800 grow-out. At the same time mortality was kcal ME/kg fed from 0 – 70 d was there reduced reduced from 20% to 4%, and so feed efficien- growth rate. In this study a single diet of 18% CP cy was actually superior with the mash diet. With and 2800 kcal ME/kg appeared to be the most eco- low nutrient dense diets growth rate is more great- nomical. Carcass yield and breast meat yield were ly affected by using mash diets, where 70 d not different for all but the 16% CP diet. As shown males are some 5 – 6 d behind schedule. in Table 5.25, mortality declined as nutrient Although there are logistical problems when using density declined, yet even with just 16% CP mash diets in mechanized feeders and microbial and 2800 kcal ME/kg there was over 10% mor- control may be more difficult, adapting feed tality to 70 d. Regardless of diet nutrient densi- texture seems to have great potential in growing ty, we have been unable to reduce mortality very heavy male broilers. below 10% without recourse to using mash diets. It seems as though regardless of nutrient f) Feed withdrawal density, the broiler is able to increase its intake of pelleted feed, and this undoubtedly con- The current major concern about feed with- tributes to high mortality. In order to reduce mor- drawal relates to microbial contamination dur- tality this voracious appetite has to be controlled, ing processing. Regardless of withdrawal time, and this can be achieved quite easily by offering the gut will retain some digesta, and this can con- mash, rather than pelleted diets (Table 5.26). taminate birds during transportation as well as the scald water during processing. Also if the intes- Table 5.26 Performance of male tines are broken during evisceration there is broilers to 70 d when fed mash vs. potential for contamination. pellet diets Withdrawing feed 6 – 8 hr prior to catching Body Wt. F:G3 Mortality seems to be optimum in terms of the bird clear- 70 d (g) (%) ing the upper digestive tract and so reducing the chance of contamination and for ease of processing High density1 3850 2.31 4.2 gizzards. The bird will lose weight during feed with- 4166 2.44 20.0 drawal, and this will average about 10 g/hr Mash depending on age and liveweight. A significant Pellets portion of this loss will be excreta evacuation by the birds. The loss in eviscerated carcass weight Low density2 3571 2.45 5.8 is closer to 2 g/hr, with equal losses to breast and 4111 2.50 12.5 leg/thigh meat. Feed withdrawal does not seem Mash to have major effects on blood or liver glucose or Pellets glycogen levels, and this may be the reason for there being fewer post-mortem changes such as PSE as 1 20% CP:3100 Kcal/kg ME, starter (0-21 d); occurs with pigs and sometimes turkeys. 18% CP:3100 Kcal/kg ME, grower (21-49 d); 16% CP:3200 Kcal/kg ME, finisher (49-70 d). In addition to the concern about gut fill at pro- 2 18% CP:2900 Kcal/kg ME (0-70 d) cessing, there is now interest in the pathogen load 3 Adjusted for mortality of the digestive tract. The ceca have a very high bacterial load and some of these will be Adapted from Leeson et al. 2000 Feeding high nutrient dense mash vs. pelleted diets reduced growth rate by about 300 g to 70 d, which represents just 2 – 3 d prolonged SECTION 5.2 Feeding programs

256 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS pathogens of concern regarding food safety. In expected standard weight. There is some com- a recent study, broilers were held on the litter or pensation when feed is reintroduced, with birds in crates for 24 hr without feed and surprising- eating up to 300 g in the first 24 hr following refeed- ly there was little change in pH of the cecal con- ing. Depending upon time of feed outage rel- tents or the bacterial populations. In fact, there ative to eventual withdrawal, means the bird can were few lactic acid producing bacteria, which have excessive quantities of digesta throughout is a situation that allows pathogens to flourish. the intestine. Excessively long periods of feed withdrawal The other aspect of late cycle broiler nutri- seem to actually increase the pathogen load in tion is potential for reducing nutrient levels, the upper digestive tract. With 12 hr+ of feed with- and particularly the inclusion of trace minerals, drawal, there are often high counts of vitamins and various feed additives. Broilers seem Campylobacter in the upper digestive tract, and most responsive to total withdrawal of vita- again this is associated with a reduction in the pres- mins, than to removal of trace minerals (Table 5.27). ence of lactic acid producing organisms. With prolonged feed withdrawal, broilers are more like- Table 5.27 Broiler growth and F:G ly to eat litter and this seems to be the source of from 42 – 49 d in response to vitamin the pathogens. Because problems are often and trace mineral supplementation correlated with reduced populations of Lactobacilli type organisms, there is interest in offering birds Vitamins Minerals Growth lactic acid in the water during feed withdrawal. (g) F:G Water with 0.5% lactic acid has been shown to ++ reduce the incidence of Salmonella and +- 564 2.41 Campylobacter in the upper digestive tract by at -+ 562 2.40 least 80%. -- 537 2.58 481 2.85 A more serious concern arises if birds are acci- dentally without feed for 12 hr+ in the 2 - 3 d prior Adapted from Maiarka et al. 2002 to feed withdrawal. Broilers again are seen to eat litter, drink excessive amounts of water and Feed efficiency and growth are both com- so produce very wet manure. Both sexes have promised by total withdrawal of vitamins from the been observed to lose up to 100 g body weight feed, and this effect is accentuated when trace min- after 18 hr of no feed being available. Coupled erals are also removed. There is also concern with with a potential growth of 70 – 80 g in this peri- higher mortality when vitamins and minerals are od, means that birds are at least 170 g behind withdrawn under heat stress conditions (Table 5.28). Table 5.28 Removal of vitamins and trace minerals from heat-stressed (24-35˚C) broilers Vitamins Minerals 35-49 d wt gain (g) F:G Mortality (%) 1280a ++ 1240b 2.66a 9.6 2.86b 13.2 -- Adapted from Teeter (1994) SECTION 5.2 Feeding programs

CHAPTER 5 257 FEEDING PROGRAMS FOR BROILER CHICKENS There are inconsistent reports on the effects anticoccidials seem to influence proliferation of of removing anticoccidials and growth promot- necrotic enteritis, then if growth promoters are not ers during the last 5 – 10 d. This situation prob- used in a feeding program, removal of ionophores ably relates to health status of individual flocks, for an extended period can compromise bird and level of biosecurity etc. Since many ionophore health and performance. 5.3 Assessing growth and efficiency a) Broiler growth eralization, maintenance energy requirement increases by about 3% for each 1˚C decline in W ith yearly increases in genetic poten- environmental temperature below 30˚C. If tial, standards for growth rate become maintenance represents 60% of total energy quickly dated. Over the past 20 needs, then feed intake is expected to change by years, there has been at least an annual increase about 2% for each 1˚C change in temperature. of 25g in body weight at 42 d of age, and in cer- Under commercial conditions stocking density tain periods we have seen gains of 30 – 50 g each is going to be one of the major variables affect- year. This growth rate is fueled by feed intake. With ing growth and feed intake (Table 5.29). increasing growth rate, there has been ever increasing efficiency of gain. It seems unlikely that With a higher stocking density, birds eat less the bird has increased its ability to digest protein, feed, presumably due to greater competition at the amino acids and energy from commonly used ingre- fixed number of feeders. However this slightly dients, and so, change in efficiency is simply a con- reduced growth is often accepted since there is sequence of reduced maintenance need. While greater liveweight production from the broiler house. there has to be a biological limit to growth rate, it is likely that management concerns will be It is generally assumed that broilers hatched from the issue that imposes a lower limit on market age. larger eggs will grow more quickly than those hatched For example, there is now concern on the ‘matu- from small eggs. As broiler breeders get older, they rity’ of the skeleton of female broilers destined for produce larger eggs and so broiler growth is often the 1.75 kg market, where market age could be correlated with breeder age. In a recent study, we 30 d or less within the next 5 – 7 years. hatched broilers from breeders at 28, 38, 48 and 58 weeks of age, and grew them under standard Factors influencing feed intake have the sin- conditions within the same broiler facility. gle largest effect on growth rate. Birds eat more Interestingly, the growth of female broilers was most in cooler environments and vice-versa, although highly correlated with breeder age (Table 5.30). this situation is confounded with humidity, acclimatization and stocking density. As a gen- Table 5.29 Influence of stocking density on broiler performance Density (birds/m2) 49 d B.wt. (g) Feed intake (g) kg/m2 10.5 2337b 4973b 23.4a 13.5 2261a 4803a 28.9b Adapted from Puron et al. (1997) SECTION 5.3 Assessing growth and efficiency

258 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.30 Broiler growth characteristics as affected by breeder age Male broiler: 28 Breeder age (wks) 58 38 48 49 d live wt. (g) 3186 3273 0 – 49 d F:G 1.88 3249 3221 1.96 49 d carcass wt. (g) 1.80 1.86 - Deboned breast wt. (g) 2498 - 587 2562 2610 605 607 Female broiler: 2595 2633 2667 2712 2.11 1.95 2.01 2.00 49 d live wt. (g) - 0 – 49 d F:G 1972 2028 2118 - 49 d carcass wt. (g) 462 468 492 Deboned breast wt. (g) Table 5.31. Change in broiler live weight and carcass weight per 1 g increase in breeder egg weight Male broiler (49 d) Live weight Carcass weight Female broiler (49 d) + 5 g/g egg wt. +11 g/g egg wt. + 8 g/g egg wt. +14 g/g egg wt. There was a significant linear trend over time While growth rate is of prime economic and from these data we can predict that both importance, uniformity of growth is becoming of liveweight and carcass weight will be influenced increasing concern. With mechanized feeding sys- by differences in egg weight that result as a con- tems, small birds have difficulty reaching feed and sequence of increased breeder age (Table 5.31). water as they are raised to best suit the flock mean growth rate. The current lack of uniformity Larger eggs usually have larger yolks, and it however, seems to start as early as the first week is often suggested that yolk size is the factor of age. Even in well-managed flocks, there is skewed influencing growth as shown in Tables 5.30 and distribution of that body weight, with a prepon- 5.31. However, experimental removal of yolk mate- derance of smaller chicks (Figure 5.5). rial from an incubating egg has little effect on chick size at hatch. Removal of albumen does however Fig. 5.5 Distribution of chick weight in a cause reduction in chick size, and so perhaps it well managed broiler flock. is the albumen content of large eggs that influences chick size and subsequent broiler growth. However, a confounding effect is that yolk size does influence the size of the residual yolk at hatch, and this may have some effect on early growth if chick placement is delayed. SECTION 5.3 Assessing growth and efficiency

CHAPTER 5 259 FEEDING PROGRAMS FOR BROILER CHICKENS When specific health problems occur, such There is a suggestion that yield of yolk and as ‘feed passage’ or ‘stunting-runting syndrome’ albumen is not highly correlated with egg size. then the weight distribution is heavily biased towards small chicks (Figure 5.6). b) Feed efficiency Fig. 5.6 Distribution of chick weight in a A measure of the efficiency of feed utiliza- floor unit with obvious health problems. tion is obviously of economic importance. Classical feed efficiency is calculated as feed intake In most flocks today there is a skewed dis- ÷ body weight, while the converse measure of tribution of 7 d body weight with the unevenness body weight ÷ feed intake is often used in contributed by 12 – 15% of small chicks. This Europe. Feed is used by the bird for two basic type of uneven distribution occurs even with hatch- reasons, namely for growth and for mainte- es of eggs from individual breeder flocks. This nance. In young birds most feed is used for growth early loss in uniformity influences subsequent flock (80%) and little is used for maintenance (20%) characteristics. and so efficiency is very good. Over time effi- ciency deteriorates because the broiler has an ever- Each 1 g change in 7 d body weight alters increasing body mass to maintain. Table 5.32 18 d body weight by 3 g (i.e. a chick that is 30 shows expected changes in classical feed efficiency g underweight at 7 d will be 90 g underweight related to age of bird. at 18 d. By 49 d the correlation is 1 g @ 7 d 5 g @ 49 d. These data suggest that at around 1.75 kg body weight, feed conversion will increase by 0.01 units It is well known that chick size is influ- for each day of growth or that conversion will enced by size of the hatching egg. A range of egg increase by 0.013 units for each 100 g increase weights are set, but usually the extremely small in market weight. As the bird gets heavier, and very large eggs are discarded. The current these units of change increase (Table 5.32). variance therefore occurs within the range of set- table eggs. The effects seen in Figures 5.5 and Over the years we have seen a steady decline 5.6 are made worse when broiler flocks are in classical feed conversion from around 2.2 in derived from a number of different age breed- the early 1960’s to 1.75 today under certain sit- er flocks. However the problem is not fully uations. This continually improving situation is resolved when eggs are graded prior to setting. due to improved genetic potential, and the fact that more feed is directed towards growth (and less for maintenance) as days to market decline. Body weight is a consequence of feed intake, and so feed intake tends to be the main variable in assessing feed efficiency. Historically broilers were grown to 45 ± 3 days and fed diets with ener- gy levels that were standardized across the indus- try. Under these conditions, the measure of clas- sical feed efficiency is useful, and should relate directly to economics of production. Today, the SECTION 5.3 Assessing growth and efficiency

260 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.32 Adjustments to feed efficiency based on body weight or age Weight Change in F:G per Daily change in category 100 g body wt. F:G 1.75 kg 0.013 0.010 2.50 kg 0.015 0.014 3.50 kg 0.017 0.016 Table 5.33 Performance and economic considerations of feeding broilers diets of varying nutrient density Mean diet energy1 Relative feed 45 d male body wt Feed:Gain Relative feed (kcal/kg) cost (kg) cost/bird 2.10 3000 100 2.7 2.00 100 3100 105 2.7 1.90 99 3200 114 2.7 1.80 102 3300 123 2.7 105 1 all other nutrients tied to energy industry grows birds over a vast range of ages/mar- ure of feed utilization is efficiency of energy use. ket weights, and there is now considerable vari- When efficiency is based on energy, the energy ation in diet nutrient density. The fact that a clas- level of the diet is irrelevant, and so this major vari- sical feed efficiency of 1.9 is achieved with a certain able is resolved. Table 5.34 indicates expected flock, has to be qualified in terms of sex of energy efficiency in male and female broilers. bird, market age and diet nutrient density. The lowest numerical feed efficiency may therefore Table 5.34 Energy efficiency in not be the most economical (Table 5.33). broilers As nutrient density increases, feed conversion predictably declines. However, body weight is Market age (d) Energy intake unaffected. Since high nutrient dense diets cost Mcal/kg gain more, the feed cost per bird will only be reduced Male Female if birds eat correspondingly less feed. In this example, the most economic situation arises 35 - 5.35 with mean energy level at 3100 kcal/kg, even though classical feed efficiency is not optimized. So 42 5.39 5.83 called ‘broiler growth models’ today should be able to identify the most profitable diet, given feed price, 49 5.84 6.28 broiler prices, expected performance, etc. The diet is ultimately least-costed in the traditional way, but 56 6.30 6.80 this prior selection is often referred to as ‘maxi- mum profit formulation”. A more useful meas- 63 6.63 - Assesssment of efficiency can be taken further than the level of individual bird production to accom- modate such factors as feed cost, carcass yield and stocking density. In the future we may even have to consider manure management in our assessment of production criteria (Table 5.35) SECTION 5.3 Assessing growth and efficiency

CHAPTER 5 261 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.35 Future considerations in assessment of efficiency of feed usage in broiler production Criteria Measurement Comments Energy efficiency Energy intake: weight gain Feed cost Energy is the most expensive nutrient, and Carcass yield Feed cost: weight gain so this value is important. To some extent, values are independent of feed intake. Bird placement Energy intake: carcass wt. Energy intake: breast meat Takes into account the fact that the most Environment Feed cost: carcass wt. expensive diet is not always the most profitable. Feed cost:breast meat Feed cost/kg bird/sq. meter Takes into account the fact that birds of similar floor space/yr weight may not always yield the same amount Economic return/sq. meter of edible carcass. floor space/yr Nitrogen excretion/bird Optimizes the use of the building e.g.: higher Phosphorus excretion/bird nutrient dense diets give faster growth rate, therefore more crops per year. Future considerations for environmental stewardship. 5.4 Nutrition and environmental temperature a) Bird response M ost broiler farms will be subjected to perform reasonably well. On the other hand, most heat stress conditions for at least part broilers are stressed at 38˚C (100˚F) when fluc- of the year. The terms heat stress or tuating day/night temperatures exist. In the fol- heat distress are used to describe the conditions lowing discussion, it is assumed that fluctuating that affect broilers in hot climates. Because conditions occur, because these are more com- birds must use evaporative cooling (panting) to mon and certainly more stressful to the bird. lose heat at high temperatures, humidity of the air also becomes critical. Consequently, a com- A market weight broiler produces about 5 – bination of high temperature and humidity is much 10 kcals energy each hour. This heat, which is more stressful to birds than are situations of generated by normal processes in the body, high temperature coupled with low humidity. must be lost to the environment by convec- Other environmental factors, such as air speed tion, conduction and/or evaporation. The broil- and air movement, also become important. It er will conduct heat from its body to whatever is also becoming clear that adaptation to heat stress it touches, assuming that these objects (litter, etc) can markedly influence broiler growth. For are at a lower temperature than is body temperature example, broilers can tolerate constant envi- (41˚C). The broiler will also convect heat away ronmental temperatures of 38˚C (100˚F) and from its body, through circulating air, again SECTION 5.4 Nutrition and environmental temperature

262 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS assuming that the air temperature is less than body of energy are lost for each gram of water evapo- temperature. The balance of heat production and rated during breathing. A market weight broiler heat loss is such that body temperature is main- producing 200 kcals heat energy per day needs tained at around 41˚C. almost 400 grams water loss by evaporation. This is an extreme case, because other heat dis- Interestingly, under thermoneutral condi- sipation mechanisms are also active and the bird tions, body temperature has little influence on also loses some water via the urine. However, this performance. However, as body temperature gets simple calculation does emphasize the need for much above 41.5˚C for broilers under heat dis- increased water intake during excessive heat tress, then there is good correlation between rise stress. Unfortunately, the situation is made worse in body temperature and decrease in perform- by the fact that cooling mechanisms, such as ance. Much above 42˚C mortality is inevitable. panting, generate significant quantities of body heat. In fact, it has been calculated that panting intro- In order to dissipate more and more heat, evap- duces an extra 20 – 25% heat load on the bird. orative cooling has to be increased. Water bal- ance and evaporative water loss of the broiler under The major heat load in the body arises from non-heat stress conditions changes over time. the digestion and metabolism of food. A simple In the first week of life, about 35% of total water way of avoiding heat stress, therefore, is to intake is excreted through evaporative losses. remove feed. Under less stressful conditions, we By seven weeks of age, this amount increases to are interested in maintaining growth rate close 70%. This increased emphasis on evaporative water to genetic potential, and this means feeding at loss with age is one of the reasons why the older close to normal physical intake. However, dif- bird has more problems in balancing its heat ferent nutrients produce different quantities of load during heat stress, because evaporative sys- heat during metabolism. For example, the tems are so heavily relied upon under normal con- metabolism of fat is most efficient, and metab- ditions. The bird does not have sweat glands, and olism of protein is least efficient in this respect. so at high temperatures, evaporative cooling is the Unfortunately, the metabolism of all nutrient is only effective means of greatly increasing heat loss. far from being 100% efficient, and so even for As the bird pants under heat stress conditions, water dietary fats, there will be some heat evolved dur- vapour is lost in the exhaled air with each breath. ing normal metabolism. Some heat is lost in raising the temperature of exhaled water vapour, from ambient (drinking water This means that diet formulation can be used temperature) to that of body temperature. However, to advantage in trying to minimize heat load. this heat loss is insignificant in relation to the heat Unfortunately, the major heat load is going to be loss needed to evaporate water. About 0.5 kcals a consequence of feed intake per se (Table 5.36). SECTION 5.4 Nutrition and environmental temperature

CHAPTER 5 263 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.36 Energy balance of a 2 kg broiler (kcal/bird) 24˚C environment: 0g Feed/day 50 g 100 g 150 g Heat production 192 Sensible loss 160 204 212 236 Evaporative loss 44 -12 168 180 192 Balance 40 44 48 -4 -12 -4 35˚C environment: 196 220 240 248 88 112 96 132 Heat production 72 88 92 96 Sensible loss 36 20 52 20 Evaporative loss Adapted from Wiernusz and Teeter, (1993) Balance Table 5.37 Male broiler feed intake at 15-30˚C Male broiler (g feed/bird/day) Age (d) 15˚C 20˚C 25˚C 30˚C 14 78 72 65 59 21 120 110 100 90 28 168 154 140 126 35 204 187 170 153 42 240 220 200 180 49 264 242 220 194 At 24˚C, the broiler is in near perfect balance, Broilers will acclimate to warm conditions with heat production being similar to heat dis- and can perform reasonably well at constant tem- sipation. At 35˚C, the broiler is in severe pos- peratures as high as 36˚C. However, if broilers itive energy balance, where heat dissipation can- are normally held at 25˚C a sudden change in not match the heat load generated by feed temperature to 36˚C may prove fatal, and will metabolism. In this situation, the broiler has to certainly influence growth rate. There is some quickly correct the balance, and the easiest research to suggest that intentionally subjecting solution is to reduce heat load by voluntary reduc- young broiler chicks to high temperatures tion in feed intake. Such changes in feed intake enables them to better withstand subsequent heat will occur very quickly, certainly within hours, stress conditions when they are older. Such accli- because the birds must maintain the balance at mated birds seem to show less of an increase in close to zero. Table 5.37 shows the expected their core body temperature when later (up to 4 feed intake of male broilers housed at varying – 6 weeks) exposed to high temperatures. Heat environmental temperatures. acclimatized birds do seem to drink more SECTION 5.4 Nutrition and environmental temperature

264 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS water and eat more feed under heat stress achieved. It is likely that the confounding effect conditions. Therefore, because acclimatized of ‘increased’ feed intake by acclimatized birds birds are prepared to eat more feed, this induces is responsible for variation in results of trials and a greater heat load, so this can counterbalance field studies of early life heat stress acclimatization. the effect of prior acclimatization. For prior acclimatization to be useful therefore, it seems The general growth response of male broil- necessary to combine this with some degree of ers of 500-2500 g body weight to a range of envi- feed restriction if maximum benefits are to be ronmental temperatures is eloquently shown by the data of May et al. (1998). Fig. 5.7 Effect of environmental temperature on daily growth of male broilers. 100 95 90 85 Gain/day, g 80 75 23C 25C 70 27C 29C 31C 65 60 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 Beginning weight, g Adapted from May et al, 1998 SECTION 5.4 Nutrition and environmental temperature

CHAPTER 5 265 FEEDING PROGRAMS FOR BROILER CHICKENS b) Potential nutritional associated effect of increased carbon dioxide loss intervention due to panting. There has been considerable research in this area, investigating the potential Nutritional intervention to limit the effects of of maintaining normal anion:cation balance heat stress include change in levels of nutrients, during heat-stress. However, the general con- change in ingredient composition, time of feed- sensus at this time is that acid:base balance ing and in extreme situations, removal of feed. per se is not a major factor influencing either growth rate or survival of broilers in heat stress In terms of nutrients and ingredients, the conditions. This is not to say that adding elec- level of crude protein should be minimized trolytes to the feed or water is ineffective, rather, and the level of supplemental fat increased to prac- their mode of action may be other than by alter- tical maximums. It is usually not economical to ing or maintaining acid:base balance. use constraints for crude protein that increase over- all diet cost by more than 5 – 8%. In general, It seems as though the benefit of adding economical reductions in crude protein level are electrolytes to the feed or water is simply to increase in the order of 2 – 3% (e.g. 22 20% CP). A the bird’s water intake which in turn fuels evap- major problem related to metabolism of proteins orative cooling. Various studies have been con- is the heat increment related to transamination ducted in which broilers have been given min- (rearrangement), deamination (breakdown), and eral supplements in the water, producing a excretion of nitrogen as uric acid in the urine. range of anion-cation balance. For example, both It follows therefore, that amino acid balance with- (NH4)2SO4 and NaHCO3 are effective water sup- in a diet is as important as the total level of crude plements used in trying to combat heat stress, yet protein. With 4% excess CP in a diet (due to using their ion balances are very different. The ben- poorer quality ingredients, while trying to achieve eficial effects of these supplements seem more the level of limiting amino acids), the bird’s closely correlated with their effects on water intake. heat output is increased by 8 – 10%. Protein qual- ity, therefore, becomes critical in these diets. Adding a mineral salt, such as KCl increas- es water intake and evaporative heat loss of Because energy intake is often the limiting the bird. A common treatment and/or preven- factor to growth during heat stress, it is tempt- tative measure during heat stress, is to add NaCl ing to recommend high-energy diets that con- at 0.5% to the birds’ drinking water. For broil- tain high levels of supplemental fats. Unfortunately, ers eating 100 g of feed containing 0.2% Na (0.5% the broiler is still eating to its energy requirement, salt) each day, means that birds consume 30% so simply increasing the energy concentration of their daily Na from feed and 70% of Na of a diet does not ensure a major increase in ener- from treated water. The level of water supple- gy intake. Broilers will tend to eat more ener- mentation should therefore, represent a signif- gy with higher energy diets, so it can be useful icant increase in the birds’ Na (or K) intake. to consider such a formulation change although Maintaining or stimulating water intake seems in itself this change will not correct growth to be a key factor in maintaining growth rate of depression. older broilers subjected to hot environments. In this regard, the use of drinker equipment is a fac- Acid:base (electrolyte) balance in the broil- tor (Table 5.38) er is altered at high temperatures because of the SECTION 5.4 Nutrition and environmental temperature

266 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Birds were always heaviest when using the open peak mortality due to heat stress is usually in late trough drinkers, and nipple height also influ- afternoon, which does not always coincide with enced growth. At 30˚C, the difference in growth the hottest time of the day. The late afternoon peri- for birds using open trough vs. nipples is greatly ac- od does, however, coincide with the time of peak centuated. The actual reason behind better growth heat of digestion and metabolism for birds eat- with open trough drinkers is not fully resolved. It ing substantial quantities of feed in the early-mid is likely that birds drink more water, but they also morning period. Consequently, it is often rec- may immerse their wattles in open trough drinkers ommended to withdraw feed prior to antici- and this aids evaporative cooling. However, pated time of peak environmental temperature, nipple drinkers are often preferred, since litter con- to minimize the heat load of the bird. dition is easier to manage. Nipple height is also critical for optimum water intake. As a rule-of- A common management scenario is to thumb nipple height should be at 10 cm at day remove feed at 10 a.m. and re-feed at 5 p.m. Such of age, and then increase by 5 cm per week. a system assumes having some supplemental lights so that they can eat at cooler times of the day. In situations when broiler mortality is the main Table 5.39 summarizes recommendations for feed concern, the best recourse is to remove feed, so formulation and feeding management for heat as to reduce heat load on the bird. The time of stressed broilers. Table 5.38 Broiler growth at 25˚C vs 30˚C using open trough or nipple drinkers (g/bird) Water system 25˚C 30˚C 28 d 49 d 28 d 49 d Open trough 1424a 3275a 1349d 2632d Low nipple 1411b 3199b 1336e 2395e Medium nipple 1400b 3164b 1333e 2300f High nipple 1385c 2995c 1303f 2104g Adapted from Lott et al. (2001) SECTION 5.4 Nutrition and environmental temperature

CHAPTER 5 267 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.39 Strategies for reducing the impact of heat stress Strategy Activity Feed formulation 1. Reduce crude protein by 2 – 3%. Feed management 2. Maintain levels of Meth + Cys, Lysine and Threonine. 3. Increase diet energy by direct substitution of 2% fat for 2% of major cereal. Bird management 4. Add 250 mg Vitamin C/kg diet. 5. Use only highly digestible ingredients. 6. Select appropriate anticoccidials. 1. Withdraw feed 10 a.m. – 5 p.m. 2. Ensure adequate feeder space and drinkers. 3. Manage nipple height according to bird age. 4. Add 0.5% salt to the drinking water. 5. Keep drinking water as cool as possible. 1. Increase air flow at bird level. 2. Maintain litter quality. 3. Use lower stocking density. 4. Do not disturb birds at time of peak heat distress 5.5. Nutrition and lighting programs L ighting programs are now used routine- in wild birds during the fall. Broilers subjected ly in growing broilers, and in some to long periods of darkness will produce more European countries it is mandatory to give melatonin, and this is thought to be involved in broilers a period of darkness. An extended some way with the beneficial effects of such light period of darkness each day seems to reduce the programs. Adding synthetic melatonin to the diet incidence of SDS and leg problems, and in of broilers does cause a calming effect, but does winter months may help to control ascites in heav- not seem to have any influence on mortality. The ier males. The major advantage to these light main feature of a lighting program for an imma- programs is a period of rest and/or tempering of ture bird such as the broiler is simply that during growth rate, which both seem to improve livability. darkness, birds are more reluctant to eat, and so There may also be some subtle effects of light this controls growth rate. that influence the bird’s metabolism. In addi- tion to influencing sex hormone output in If one visits 20 different broiler farms, it is pos- mature birds, light also affects the pineal gland sible to see 20 different lighting programs. at the base of the brain, and this is responsible However, all have the common feature of impos- for production of another hormone, namely ing a long period of darkness that lasts for at least melatonin. Melatonin is produced during long 8 hours. Differences occur in the ages at which periods of darkness, and is the hormone respon- the light restriction is initiated and the pattern of sible for shutting down the reproductive system returning to a longer daylength. SECTION 5.5 Nutrition and lighting programs

268 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Broilers are reluctant to eat in the dark, and While broilers will be smaller during the so the major ‘activity’ during darkness is simply period of extended darkness, they are able to com- sitting. However, some birds will attempt to eat pensate by 49 d. Mortality is reduced, and espe- and drink at this time and this disturbance can cially the incidence of leg disorders. Although often cause scratching and downgrading of the carcass. not statistically significant, there is usually a Such problems, which lead to infection, will be slight reduction in breast meat yield for broilers more prevalent with high stocking densities, on reduced daylength as shown in Table 5.40. and when longer (> 8 hr) periods of darkness are used after 22 – 25 days of age. The shorter the As previously mentioned, there are many period of light the greater the reduction in feed different light programs, and selection depends on intake, and so the greater the control over sex of bird, diet nutrient density, pellet quality, mar- growth. If birds are kept on constant short days ket weight and whether or not blackout or open- to 49 d (i.e. no compensatory step-up) then sided housing is used. In addition, the extended growth rate will be reduced. On average, for each period of darkness may be less severe or shortened 1 hour of darkness, broiler growth will be somewhat in the summer vs. winter, since hot weath- reduced by 20 g. Therfore, keeping birds on con- er also reduces growth rate, and the two combined stant 12 hr vs. constant 24 hr from 1 – 49 d, will can cause delay in grow-out. Table 5.41 summarizes reduce growth by about 240 g. However, the the factors influencing choice of light program. Table reduced growth will be accompanied by reduced 5.42 shows examples of lighting programs taking mortality. In practice, it is more common to step- these factors (Table 5.41) into account. up the hours of light after 2 – 3 weeks, and this allows for growth compensation. Light intensity can also influence bird activ- ity and feed intake. The higher the intensity, There is little doubt that short-day lighting pro- usually the greater the bird activity and so this can grams are most beneficial for male broilers. lead to more maintenance costs, and poorer They are particularly successful for males grown feed efficiency. Higher body weights and better to heavier weights and less useful (and perhaps feed efficiency have been recorded at 5 vs. 150 detrimental) to lightweight females. Table 5.40 lux. Light intensity after brooding should be at 2 shows typical research results for 49 d male – 5 lux, which is the minimal intensity for the stock- broilers. person to adequately inspect birds and equipment. Table 5.40 Effect of step-down, step-up lighting for male broilers Treatment 49 d B. wt. F:G Mortality Leg problems Breast yield (kg) (%) (%) (%) 23L:1D 1.85 Step-down:Step-up 2.86 1.86 8.5 20.0 24.8 2.82 3.0 9.5 24.2 Adapted from Renden et al. (1996) SECTION 5.5 Nutrition and lighting programs

CHAPTER 5 269 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.41 Factors influencing choice of light program Parameter Consideration for light:dark schedule 1. Strain of bird Earlier fast growth means need for earlier introduction of reduced daylength. 2. Diet nutrient density With higher nutrient density there is more benefit to a longer 3. Pellet quality and more extended period of darkness. 4. Market weight 5. Open sided vs. blackout housing The better the pellet quality, the greater the need for light control. 6. Season For older, heavier birds, delay step-up schedule. Open-sided housing dictates the maximum period of darkness. With blackout housing there is absolute control over duration and intensity of light period. Less severe programs in hot weather because growth-rate is already reduced. Table 5.42 Examples of light programs for birds grown to 42 or 56 d in either summer or winter, in open or blackout houses (hours light/day) Age (d) Black out Winter Summer Open-sided Winter Summer 42 d 56 d 0–5 42 d 56 d 42 d 56 d 42 d 56 d 5–8 23 23 8 - 12 23 23 12 10 23 23 23 23 12 – 16 14 12 12 10 16 – 20 14 12 14 12 Natural Natural Natural Natural 20 – 24 14 12 14 12 24 – 28 16 14 16 14 Natural Natural Natural Natural 28 – 32 16 14 16 14 32 – 36 18 16 18 16 14 Natural Natural Natural 36 – 40 18 16 18 16 40 – 44 18 16 18 16 16 14 14 Natural 44 – 48 18 18 18 18 48 – 52 18 18 - 18 16 14 14 14 52 - 56 - 18 - 18 - 18 - 18 18 16 16 14 - 18 18 16 16 16 18 16 16 16 18 18 18 16 18 18 18 16 - 18 18 18 - 18 - 18 - 18 - 18 SECTION 5.5 Nutrition and lighting programs

270 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS There is little information available on the Short cycles of light and dark are repeated effect of color (wavelength) of light on broilers. It throughout the day, the most common being eight seems as though wavelengths above 550 nm (pur- cycles of 1 hr light:2 hrs darkness. The idea behind ple-orange-red colors) cause reduced growth rate. the program is that birds will eat during the On the other hand, shorter wavelengths, at the blue- light period and then sit down during the 2 hr green end of the spectrum produce increased dark cycle and be ready to eat again when growth rate. These effects are quite subtle (5% max- lights return. Obviously adequate feeder space imum) yet it is conceivable that light color could is essential with the program and it is only be used to either slow down or speed up growth viable with black-out housing (Table 5.43). rate at specific times during grow-out. Currently bulbs that produce light at a specific wavelength With intermittent lighting, it is assumed that e.g. red or green, are very expensive. energy efficiency will be improved, since birds are inactive for 66% of the day. In the study Intermittent lighting is another option for detailed in Table 5.43, there was greater overall managing broilers, although unlike the step- heat production for birds on the 1L:2D pro- down step-up programs described previously, this gram, and so increased growth was simply a fac- system is intended to stimulate growth rate. tor of increased feed intake. Table 5.43 Male broiler growth with intermittent vs. continuous lighting Body weight (g) Lighting 21 d 42 d 56 d 0 – 56 d F:G Continuous 717 2393 3459 2.07 1 hr L: 2 hr D 696 NS 2616 3637 2.03 * ** NS Adapted from Ohtani and Leeson (2000) 5.6 Nutrition and gut health products will be developed, and so one sce- nario is that at most, only currently registered prod- Bacterial and parasitic infections of the ucts will be available. gastro-intestinal tract are an ever present threat to broilers grown on litter floors. The We are greatly hampered in the study of microbial status of the tract is kept in balance by gut health by not knowing, with any great pre- use of anticoccidials in conjunction with so- cision, the normal microflora present in healthy called growth promoters. The mode of action of birds. It has been suggested that, at best, con- growth promoters has never really been fully ventional culture techniques are isolating 50% explained, yet when they are excluded from the of the species of bacteria present in the gut. Newer diet, bacterial overgrowth can occur. The role of techniques involving DNA fingerprinting of gut health in broiler performance has suddenly microbes may give us a better understanding of become topical because of current or pending leg- the complexity of the microflora, and in partic- islation concerning use of antibiotics in poultry ular, how they change in response to various diet diets. With the current pressure on antibiotic use in animal diets, it seems less likely that new SECTION 5.6 Nutrition and gut health

CHAPTER 5 271 FEEDING PROGRAMS FOR BROILER CHICKENS treatments. On the other hand, we are aware Rapid early development of the intestinal of the major pathogens, and as a starting point epithelium is also another prerequisite for nor- in maintaining gut health, it is more promising mal digestion. The villi and microvilli grow in the short-term to concentrate on their control. rapidly in the first few days, and any delay in this process is going to reduce nutrient uptake. The chick hatches with a gut virtually devoid Presence of pathogens, mycotoxins and ani- of microbes, and so early colonizers tend to pre- mal and plant toxins will all delay microvilli devel- dominate quite quickly. The enzyme system and opment. Selection of highly digestible ingredi- absorptive capacity of the newly hatched chick ents, devoid of natural toxins where possible, is is also quite immature. As previously described therefore important for rapid early gut development. in section 5.2b, selection of ingredients eaten by As the epithelium develops within the microvil- the chick in the first few days of life will undoubt- li, where mucus is secreted and this acts as an edly influence microbial growth and perhaps important barrier against pathogenic coloniza- microbial species. Any undigested nutrients tion and also auto digestion from the bird’s will be available to fuel microbial growth in the own digestive enzymes. Some bacteria are lower intestine and ceca – if these happen to able to colonize because they are able to break- include pathogens, then the chick will be dis- down this protective mucus layer. Heliobacter advantaged. The ‘normal’ gut microflora devel- pylori, the bacteria that causes gastric ulcers in ops quite quickly, and so microbial numbers and humans, secretes urease enzyme that destroys species present on the hatching tray, in the the protective mucus coating, thereby making the hatchery, during delivery, and the first few days stomach wall susceptible to degradation by at the farm will likely dictate early colonization. hydrochloric acid and pepsin. It would be While ‘dirty-shelled’ eggs may hatch quite well, interesting to study the gut microflora of birds fed they do provide a major source of microbial col- high urease soybean meal. onization for the hatchling. In addition to capturing digested nutrients, the The Nurmi concept of manipulating gut epithelium of the gut also secretes large quanti- microbes relies on early introduction of non-path- ties of water that aid in digestion. For each ogenic microbes. Ideally, these microbes will help gram of feed ingested, up to 2 ml of water may prevent subsequent pathogenic colonizations. be infused into the gut lumen, and this will sub- Today, there is not an ideal culture for such a com- sequently be resorbed in the lower intestine. If petitive exclusion product, which is again a the epithelium is damaged by pathogens or tox- factor of our not knowing the profile of a healthy ins, then it can become a net secretor of water, microflora. In the past, undefined cultures have and this contributes to diarrhea type conditions. been used with reasonable success, but now reg- Some strains of E. coli can also secrete toxins that ulatory agencies are insisting on dosing birds only disrupt water balance and contribute to diarrhea. with accurately defined cultures. It seems that Rancid fats also contribute to diarrhea by caus- if competitive exclusion (CE) is to be successful, ing sub-lethal injury to the microvilli epithelium cultures must be administered as soon as pos- sible, and time of placement at the farm may be Without the use of antibiotic growth promoters, too late. However CE is undoubtedly going to the incidence of necrotic enteritis and coc- be one of the management tools routinely used cidiosis are often the main production con- in broiler production. cerns. It now seems obvious that one of the major SECTION 5.6 Nutrition and gut health

272 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS modes of action of growth promoters is control normal site of adhesion in the small intestine. over necrotic enteritis caused by Clostridium per- Coupled with increased incidence of NE, so fringens. The association between coccidiosis called ‘dysbacteriosis’ is now common in and necrotic enteritis may be as simple as coc- European broiler operations, and represents cidial oocysts damaging the gut epithelium and abnormal microbial overgrowth in the absence so allowing for greater adhesion of clostridial bac- of antibiotic growth promoters. This latter con- teria. There is no doubt that judicious use of dition does not seem to be related to diet com- ionophore anticoccidials or coccidial vaccines position or ingredient selection. Necrotic enteri- are important in the control of necrotic enteritis. tis is also more common if the diet contains pectins contributed, for example, by ingredients such as There has been a significant increase in the rye. While rye is not a common component of incidence of necrotic enteritis (NE) in Europe fol- broiler diets, such findings indicate that diges- lowing removal of growth promoting antibi- ta viscosity, and associated maldigestion, are otics. Unfortunately, broiler diets in Europe ideal for bacterial proliferation. There is a suggestion are often based on wheat as the major cereal and that clostridial growth is greatly reduced in diets it is well documented that clostridia multiply and containing wheat that is processed through a colonize more quickly when the diet contains roller mill, rather than a conventional hammer mill. much more than 20% wheat. An interesting obser- Table 5.44 summarizes suggestions for trying to vation in Europe is that clostridia are now col- minimize the incidence of necrotic enteritis in birds onizing the upper digestive tract as well as the fed diets devoid of antibiotic growth promoters. Table 5.44 Actions to reduce the incidence of necrotic enteritis in broilers Action Effect 1. Minimize feed changes Change in ingredient/nutrient composition is associated with change in gut microflora 2. Use highly digestible ingredients Undigested nutrients fuel bacterial overgrowth 3. Minimize the use of wheat (< 20% Increased digesta viscosity leads to greater clostridial activity. Enzyme addition important ideally) Change in digesta viscosity? 4. Process wheat through a roller mill Rancid fats injure the microvilli 5. Use only quality fats and oils Urease can destroy protective mucus barrier 6. Ensure low level of urease/trypsin Toxins can destroy epithelial cells in the microvilli inhibitor in soybean meal 7. Use ingredients with minimal levels of Coccidiosis predisposes clostridial growth mycotoxins, especially up to 28 d of age 8. Use appropriate ionophore anticoccidials or coccidial vaccines SECTION 5.6 Nutrition and gut health

CHAPTER 5 273 FEEDING PROGRAMS FOR BROILER CHICKENS Another approach to maintaining gut health broilers. In a recent study, we observed improved is microbial reduction in feed and water. There growth with using drinking water at pH 5 vs. pH is no doubt that high temperature pelleting ( 80˚C) 7.5. Interestingly, at pH 4, produced by simply can inactivate pathogens such as salmonella. using more organic acid, we observed fila- However, ‘sterile’ feed is an ideal medium for sub- mentous yeast growth in the water lines, and this sequent bacterial colonization (since there is no impacted water intake by clogging nipple competition for growth) and so a practical prob- drinkers. Yeast are always present in poultry facil- lem is to prevent subsequent recontamination ities and thrive in acid environments. between the time feed leaves the mill and is deliv- ered to the feed trough. Organic acids, such as The other alternate dietary intervention for propionic acid, can help prevent such reconta- preventing bacterial overgrowth is use of manan- mination, and where allowed by regulatory oligosaccharides. Many pathogens such as E. coli agencies, formaldehyde is especially effective attach to the gut epithelium by small appendages against colonization by salmonella. called fimbriae. These fimbriae actually attach by binding to mannose sugar receptors. If man- Drinking water is another potential route nose sugars are included in the diet, they also attach of bacterial infection. Many farms utilize some to these binding sites and effectively block system of water sanitation, such as chlorine at attachment by many strains of E. coli and 3 – 4 ppm. While such sanitizers hopefully Salmonella. Commercial products such as ensure a clean water supply at the nipple, they BioMos®, which is derived from the outer cell have no effect on gut health. Of more recent inter- wall of Saccharomyces yeast, is often used as est is the use of organic acids, such as lactic acid, part of an alternative strategy to antibiotics. as both a sanitizer and to manipulate gut pH. Such products seem most efficacious when Adjusting water pH from regular levels of 7.2 – used on a step-down program, such as 2 kg, 1 7.5, down to pH 5 with products such as lactic kg and 0.5 kg per tonne in starter, grower and acid are claimed to reduce pathogen load in young finisher diets. 5.7 Metabolic disorders tions, and/or in cool climates ascites can still be problematic and often necessitates tempering of T here has been a steady decline in the growth rate as a control measure. incidence of classical metabolic disor- ders as a consequence of genetic selection a) Ascites for liveability. Metabolic disorders such as ascites, Sudden Death Syndrome (SDS) and leg disorders Ascites is characterized by the accumulation collectively still account for the majority of mor- of fluid in the abdomen, and hence the basis for tality and morbidity in healthy flocks, although the the common name of ‘water-belly’. Fluid in the total incidence is now closer to 2 – 3 % vs. abdomen is, in fact, plasma that has seeped 4 – 5% just 10 years ago. In male broilers, SDS from the liver, and this occurs as the end result will usually be the major cause of mortality start- of a cascade of events ultimately triggered by oxy- ing as early as 10 – 14 d of age. At high eleva- SECTION 5.7 Metabolic disorders

274 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS gen inadequacy within the bird. For various rea- ly at high altitude, and comparable slower sons, the need to provide more oxygen to the tis- growth (4 – 5%) at sea level would virtually elim- sues leads to increased heart stroke volume, inate the incidence of ascites. Regions of high and ultimately to hypertrophy of the right ven- altitude invariably have cool night time tem- tricle. Such heart hypertrophy, coupled with mal- peratures (< 15˚C) and no one has really quan- function of the heart valve, leads to increased pres- titated the effects due to altitude per se vs. cool sure in the venous supply to the heart and so night temperatures. pressure builds up in the liver, and there is often a characteristic fluid leakage. Keeping birds ‘warm’ is perhaps the single most practical way of reducing the incidence of Because of the relationship with oxygen ascites. As environmental temperature changes, demand, ascites is affected and/or precipitated there is a change in the bird’s oxygen requirement. by such factors as growth rate, altitude (hypox- If one considers the thermoneutral zone fol- ia) and environmental temperature. Of these fac- lowing the brooding to be 24 – 26˚C, then tem- tors, hypoxia was the initial trigger some years peratures outside this range cause an increase ago, since the condition was first seen as a in metabolic rate, and so increased need for oxy- major problem in birds held at high altitude, where gen. Low environmental temperatures are most mortality in male broilers of 20 – 30% was not problematic, since they are accompanied by an uncommon. Today, ascites is seen in fast grow- increase in feed intake with little reduction in ing lines of male broilers fed high nutrient dense growth rate. While there is an increased oxygen diets at most altitudes and where the environment demand at high temperatures due to panting etc., is cool/cold at least for part of each day. Mortality this is usually accompanied by a reduced growth seen with ascites is dictated by the number of ‘stres- rate, and so overall there is reduced oxygen sors’ involved and hence the efficacy of the demand. Under commercial farm conditions, cardio-pulmonary system to oxygenate tissues. cold environmental conditions are probably the major contributing factor to ascites. For Although growth rate per se is the major fac- example, at 10 vs. 26˚C, the oxygen demand by tor contributing to oxygen demand, the com- the bird is almost doubled. This dramatic position of growth is also influential, because oxy- increase in oxygen need, coupled with the need gen need varies for metabolism of fats vs. to metabolize increased quantities of feed, proteins. Oxygen need for nitrogen and protein invariably leads to ascites. metabolism is high in relation to that for fat, although it must be remembered that the chick- Manipulation of diet composition and/or en carcass actually contains little protein or feed allocation system can have a major effect nitrogen. The carcass does contain a great deal on the incidence of ascites. In most instances, of muscle, but 80% of this is water. On the other such changes to the feeding program influence hand, adipose tissue contains about 90% fat, and ascites via their effect on growth rate. However, so its contribution to oxygen demand is pro- there is also a concern about the levels of nutri- portionally quite high. Excess fatness in birds will ents that influence electrolyte and water balance, therefore lead to significantly increased oxygen the most notable being sodium. Feeding high lev- needs for metabolism. At high altitude, these effects els of salt to broilers (> 0.5%) does lead to are magnified due to low oxygen tension in increased fluid retention, although ascites invari- the air. Interestingly, broilers grow more slow- ably occurs with diets containing a vast range of SECTION 5.7 Metabolic disorders

CHAPTER 5 275 FEEDING PROGRAMS FOR BROILER CHICKENS salt, sodium and chloride concentrations. Apart and obviously there is a balance between the from obvious nutrient deficiencies, or excesses degree of feed restriction and commercially as in the situation with sodium, the major acceptable growth characteristics. Using feed involvement of the feeding program as it affects restriction or restricted access time to feed, ascites revolves around nutrient density and ascites can be virtually eliminated in male broil- feed restriction. Ascites is more common when ers (Table 5.46). high energy diets are used, especially when these are pelleted. Dale and co-workers grew Although low energy diets have little appar- birds on high energy diets designed to promote ent effect on growth rate, there is often reduction rapid growth and likely to induce ascites. There in ascites. Using high energy diets with access was no correlation between 14 d body weight at 8 h/d is perhaps the most practical way of con- and propensity of ascites, although birds fed 3000 trolling ascites in problem situations. As shown in Table 5.46, elimination of ascites is at the 3100 kcal ME/kg rather than 2850 2950 cost of a 200 g or 2 d delay in growth rate. A 2 kcal ME/kg had twice the incidence of ascites. – 3 d delay in market age sounds quite a reasonable trade-off for a major reduction in ascites. However, When diets of varying nutrient density are used, careful economic analysis must be carried out to there is a clear relationship of energy level and determine the real cost of such decisions. A one incidence of ascites (Table 5.45). day delay in market age can be accepted if mor- tality is reduced by at least 2.5%. Because feeding program, nutrient density and growth rate are all intimately involved in affect- Another factor to consider in diet formula- ing the severity of ascites, then there is invariably tion is the balance and the quality of the protein. discussion on the possible advantages of feed Excess nitrogen must be removed from the body, restriction. The goal of such programs is to and this is an oxygen demanding process. There reduce the incidence of ascites without adverse- is a potential to reduce the oxygen demand ly affecting economics of production. It is through minimizing crude protein supply while expected that nutrient restriction programs will maintaining essential amino acid levels in a reduce final weight-for-age to some degree, Table 5.45 Effect of diet nutrient density and composition on incidence of ascites at 49 d Diet ME Crude protein Added Fat Ascites mort. (kcal/kg) (%) (%) (%) 2950 23 0 8.8 2950 23 4 8.7 3100 24 4 15.8 2950 21 0 9.0 2950 21 4 8.5 3100 22 4 12.0 Adapted from Dale and Villacres (1986) SECTION 5.7 Metabolic disorders

276 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.46 Incidence of ascites in male broilers fed restricted quantities of feed or limited access time to feed Diet treatment Weight gain Mortality (%) (g) Total Ascites High energy (3000 3300) Low energy (2900 3100) 2616a 12.8 3.8 High energy (8 h/d) 2607a 11.3 1.4 High energy (90% ad lib) 2422b 8.7 0.6 2452b 9.0 0.2 Adapted from Camacho-Fernandez et al. (2002) diet. If we consider two diets providing the same haps the richest sources of arginine, at around level of available amino acids, but with 20 vs. 4%. Taurine is an amino acid rarely considered 24% crude protein, then there will be a need for in poultry nutrition. It is required by cats where birds to deaminate an extra 4% CP in the high- deficiency causes heart defects somewhat sim- protein diet. If birds consume 130 g feed/d, this ilar to those seen with ascites. However, adding means an extra 5 g/d of protein for catabolism. taurine to broiler diets has no effect on growth Such protein catabolism will likely result in rate or cardio-pulmoary physiology, and with meat uric acid and fat synthesis, and these are calculated meal in the diet ‘deficiency’ is unlikely to occur. to need 2 and 1 litres of oxygen per day respec- tively. Therefore, catabolism of an extra 5 g crude If ascites mortality is sufficiently high, the protein each day means a 3 litre increase in oxy- following diet changes may be considered: gen demand, which represents about an 8% increase relative to the bird’s total requirements. • Low energy feeds throughout the entire life There is an obvious incentive to minimize crude protein per se, because its catabolism merely cycle e.g.: imposes another stress on the oxygen demand of the bird. There has been recent interest in the Starter (2850 kcal ME/kg) metabolism of two specific amino acids with poten- Grower (2950 kcal ME/kg) tial to influence incidence of ascites. Arginine Finisher (3100 kcal ME/kg) is a precursor of nitric oxide, which acts as a potent vasodilator. Feeding more arginine should • Use mash rather than pelleted feeds. therefore lessen the effects of increased pressure within the cardiovascular system. Feeding an extra Do not use too fine a mash diet, since this 10 kg arginine/tonne does, in fact, cause a dra- encourages feed wastage and causes matic reduction in pulmonary arterial pressure. dustiness at broiler level. Unfortunately synthetic arginine is prohibitive- ly expensive and no natural ingredients are suf- • Consider skip-a-day feeding from 7 – 20 d ficiently enriched to supply such high levels in the diet. Groundnut and cottonseed meal are per- of age. Longer periods of restricted feeding may be necessary where ascites levels are very high. Water management becomes more critical with this system. SECTION 5.7 Metabolic disorders

CHAPTER 5 277 FEEDING PROGRAMS FOR BROILER CHICKENS • Consider limit-time feeding, such that birds ly after death, and hence blood profiles taken from SDS birds will likely vary depending upon sam- have access to feed for 8 – 10 hours each pling time following mortality. SDS can be reduced or eliminated by nutritional or man- day. Extra care is needed in water manage- agement practices that reduce growth rate. Obviously, such decisions will have to be based ment so as to prevent wet litter. on local economic considerations. At this time, there is no indication of a single causative fac- • Use no more than 21% crude protein in tor, and diet manipulation other than that relat- ed to reduced growth rate, is usually ineffective. starter diets, 19% in grower and 17% in c) Skeletal disorders finisher/withdrawal. Most broiler flocks will have a proportion of b) Sudden Death Syndrome birds with atypical gait, although growth rate may be unaffected. There is now greater incidence Sudden Death Syndrome (SDS) has been of birds with twisted toes, yet again this is in birds recognized for over 35 years. Also referred to that achieve standard weight-for-age. Most leg as Acute Death Syndrome or ‘flip-over’, SDS is problems likely have a genetic basis, although most common in males and especially when severity of problems can be influenced by nutri- growth rate is maximized. Mortality may start tional programs. The most common skeletal abnor- as early as 10 – 14 d, but most often peaks at malities seen in broilers are tibial dyschon- around 3 – 4 weeks of age, with affected birds droplasia (TD) and rickets. The fact that leg invariably being found dead on their back. problems are more prevalent in broilers (and Mortality may reach as high as 1 – 1.5% in turkeys) than in egg-type birds, has led to the spec- mixed sex flocks, and in male flocks the condition ulation of growth rate and/or body weight as is often the major single cause of mortality, causative factors. On this basis, one is faced with with death rates as high as 2% being quite numerous reports of general nutritional factors common. The economic loss is therefore sub- influencing leg problems. For example, it has been stantial. Confirmation of SDS by necropsy is suggested that energy restriction in the first few difficult as no specific lesions are present. Birds weeks halves the number of leg problems in broil- are generally well-fleshed with partially filled crop ers, while reduced protein intake results in and gizzard. There seems little doubt that any fewer leg abnormalities. Similarly, restricting access nutritional or management factors that influ- to feeder space also seems to result in fewer leg ence growth rate will have a corresponding defects. However, most recent evidence suggests effect on SDS. Sudden Death Syndrome can vir- that body weight per se is not a major predisposing tually be eliminated with diets of low nutrient den- factor to leg problems. From experiments involv- sity although these may not always be eco- ing harnessing weights to the backs of broiler chick- nomical in terms of general bird performance. ens and poults it is concluded that severity of leg Research data suggests that diets based on pure abnormality is independent of body weight and glucose as an energy source result in much that regular skeletal development is adequate to higher incidence of SDS compared to birds fed support loads far greater than normal body starch or fat-based diets. It seems likely that some anomaly in electrolyte balance is involved in SDS and that there is a genetic predisposition to this in terms of heart arrhythmia. In part, this is due to the fact that metabolic changes occur rapid- SECTION 5.7 Metabolic disorders

278 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS weight. There seems to be some disparity cept comes from experiments involving syn- between the effects on skeletal development of thetic amino acids and purified diets. The bird’s (1) limiting the incidence by reducing the plane nitrogen requirement for optimum organic of nutrition and (2) failing to aggravate the prob- matrix development is often greater than the appar- lem by artificially increasing body weight. This ent requirement for growth. The wry neck con- apparent dichotomy suggests that it is the rate of dition sometimes seen in broiler breeders, and growth rather than body weight per se that is a especially males, may also be related to disrupted predisposing factor. amino acid metabolism. While not directly a skele- tal abnormality, the condition seems to be relat- In addition to the confounding effect of ed to the metabolism of tryptophan or niacin. genetics on skeletal development, there is also During incubation, wry neck arises in the embryo some effect of steroid hormones. Castrated because of greater muscle pull on one side of the turkeys have a higher incidence of leg abnormalities neck, which together with pressure from the than do intact toms or those treated with testos- amnion, causes the ‘apparent’ skeletal deformity. terone. It is suggested that androgens act to fuse the epiphyses and shafts of long bones. There Certain feed ingredients have been associated may well be major sex differences in the hormonal with leg disorders. Much of the early work in this control of skeletal development related to the bal- area centered on brewer’s yeast and its ability to ance of androgens:estrogens. However, the reduce leg disorders. With current interest in pro- effect of androgens:estrogens per se on skeletal biotics and other yeast-based additives, this development in the relatively juvenile broiler of idea may receive renewed attention. There are today is perhaps questionable due to the fact that isolated reports of certain samples of soybean meal little sex differentiation in tibiotarsal length is seen contributing to TD in broilers although this may until after 5 weeks of age. simply be a factor of acid:base balance of the diet. It is often suggested that use of low protein It is realized that feedstuffs contaminated with diets reduces the incidence of leg disorders certain mycotoxins can induce or aggravate although this is likely a consequence of reduced skeletal problems. Grains contaminated with growth rate. Diets high in protein can interfere Fusarium roseum have been shown to cause TD. with folic acid metabolism and in so doing, Aflatoxin and ochratoxin both decrease bone increase the incidence of leg problems. However, strength, and this may be related to vitamin D3 in recent studies involving folic acid deficient diets, metabolism. Under such field conditions birds we were unable to show an effect with 22 vs. 30% sometimes respond to water soluble D3 admin- crude protein diets. In studying factors influencing istered via the drinking water, regardless of the skeletal development in broiler breeders and level and source of D3 in the diet. Attempts at Leghorns, we have shown that while early skele- reducing leg problems by minimizing microbial tal development was little influenced by mineral contamination of the litter have met with a and vitamin fortification, shank and keel lengths varying degree of success. Adding sorbic acid could be increased by feeding diets of higher pro- to the diet, or treating litter with potassium sor- tein content (22 vs. 16% CP). It is also conceivable bate improves leg condition only in isolated that the ratio of amino acids:non-protein nitro- trials. A number of fungicides used in grain treat- gen may be of importance in the development ment can also themselves lead to leg problems. of bone organic matrix. Evidence for this con- The presence of tetramethylthiuram significantly SECTION 5.7 Metabolic disorders

CHAPTER 5 279 FEEDING PROGRAMS FOR BROILER CHICKENS increases the incidence of TD, while tetram- There is also evidence to suggest that D3 is ethylthiuram disulphide causes the ‘classical’ con- involved with collagen synthesis, where the dition of irregular penetration of blood vessels into the cartilage, which is a precursor to TD. maturation of collagen crosslinks seems D3 dose related. While 1-25 (OH)2D3 is unlikely High chloride levels induce TD, although since to be available to the feed industry, nutritionists there are no major shifts in plasma ions with TD, it is concluded that the problem is not simply relat- now have the option of using , 25(OH)2 commonly ed to defective calcification. The occurrence of referred to as Hy-D®. Since the synthesis of,25 crooked legs seems to be greater when chicks are fed diets with a narrow range of cations:anions (uOctHs )s2unchoramsaHllyy-oDc®cuarrse in the liver, then prod- and the incidence of TD and bowed legs appears going to be most ben- to increase with increase in anion content of the diet. There may be a relationship between ion eficial when liver function is impaired for what- balance and vitamin D3 metabolism. Increasing the chloride content of the diet from 10 to 40 ever reason. mEq/100 g was reported to markedly enhance cartilage abnormalities when the cation (Na+, K+) While deficiencies of most vitamins have been content of the diet was low. Thus, with excess associated with leg problems, pyridoxine has per- Cl-, chicks become acidotic, although the con- haps received the most attention. There is over- dition can be corrected with dietary sodium whelming evidence to suggest that low levels lead and potassium carbonates, suggesting that if to skeletal abnormalities and/or that supple- the diet is high in Cl-, then it must be balanced mentation reduces the incidence. It has been with equimolar concentrations of Na+ + K+ in the hypothesized that pyridoxine may exert its ben- form of readily metabolizable anions. Workers eficial effect via involvement with zinc home- from France have indicated that liver homogenates ostasis and in particular the formation of picol- from acidotic chicks lose 50% of their capaci- inic acid which is involved in intestinal zinc ty to synthesize 1,25-cholecalciferol which is the absorption. There is an apparent synergism active D3 metabolite. This possibly infers a between zinc, B6 and tryptophan involved in the relationship between acid:base balance TD, prevention of leg weakness. The situation with and vitamin D3 metabolism. pyridoxine is further complicated through the effect of diet protein as previously described with In certain situations, a deficiency of D3 will folic acid. Common to many other diet situations, mimic both Ca and P deficiency situations. pyridoxine deficiency manifests itself through epi- While Ca deficient chicks are usually hypocal- physeal lesions consisting of uneven invasion of cemic and hyper-phosphatemic, D3 deficiency irregular blood vessels into the maturing growth invariable results in hypocalcemia and hypo-phos- plate. Presumably the higher level of diet pro- phatemia. In the D3 deficient chick a greater rel- tein increases the metabolic requirement for ative P deficiency is caused by parathyroid hor- pyridoxine through such processes as transam- mone. In situations of D3 repletion, the skeleton ination and/or deamination. While deficiencies seems to respond much more slowly than does of many vitamins can therefore, precipitate leg the intestine, since the immediate effect of re-feed- problems in broilers, there is also evidence to sug- ing D3 is better ‘absorption’ of the diet Ca. gest that certain vitamin excesses may be detri- mental. Very high levels of vitamin A in the diet increase the incidence of rickets, while impaired bone formation has been observed with excess dietary vitamin E. It must be pointed out how- ever, that all these reported effects of vitamin excess SECTION 5.7 Metabolic disorders

280 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS on bone metabolism relate to dietary levels collagen secretion and this can be restored by grossly in excess (5 – 10 times) of normal feed- administration of Fe2+ or Fe2+ with Mn2+, but ing levels and hence would only be practical- not by Mn2+ alone. The agent seems to block the ly encountered under unusual circumstances. synthesis of hydroxylysine and within this mech- anism there seems to be a step requiring Fe2+. As with vitamins, deficiencies, or excesses Copper metabolism has always been suspect in of a vast range of minerals, can also influence studies of leg problems, since there are certain bone development. The effect of abnormal lev- similarities between the cartilage of copper els and/or ratios of calcium:phosphorus are deficient birds and those with TD. However, well documented. Confusion sometimes exists attempts to correct TD with supplements of Cu with respect to diagnosis of calcium or phosphorus have invariable proved disappointing. deficiencies, and accurate on-farm diagnosis Solubilization studies indicated that dystrophic of phosphorus deficiency vs. calcium excess is cartilage (TD) is not deficient in cross-linked col- difficult, and immediate recommendations of diet lagen, a situation often seen with classical cop- change can be misleading prior to complete diet per deficiency. analysis. Identical lesions for the two conditions are seen suggesting that excess calcium forms insol- Skeletal disorders are sometimes seen in uble Ca3(PO4)2 in the intestine, thereby induc- the first few days after hatching and so it is pos- ing phosphorus deficiency. Table 5.47 shows nor- sible that metabolic disorders are initiated dur- mal levels of minerals in bone ash, and so ing incubation. Skeletal mineralization starts at values which are much different to these are a around the eighth day of incubation, and at cause for concern. this time the yolk serves as a source of calcium. Shell calcium is not utilized until about the Table 5.47 Normal mineral content 12th day of incubation, although during the of bone ash course of embryonic development, the embryo will take up some 120 mg Ca from the shell. Calcium 37% Culturing developing embryos in a medium Phosphorus 18% deficient in calcium quickly results in gross Magnesium 0.6% skeletal abnormalities. There have been no 200 – 250 ppm reports linking breeder eggshell quality with Zinc 20 ppm bone formation in broiler offspring. Similarly, there Copper 3 – 5 ppm have been relatively few reports of the effect of Manganese 400 – 500 ppm breeder nutrition and management on skeletal development of the embryo. There seems little Iron doubt that more common leg problems, such as tibial dyschondroplasia (TD) are inherited to The effect of manganese deficiency on the inci- some degree and hence pedigree has a poten- dence of perosis is obviously well documented tially confounding effect on studies of leg abnor- although some evidence suggests that interac- malities. TD is related to a major sex linked tion with iron may be a complicating factor. gene, the recessive of which is associated with Administration of hydralazine, a manganese a higher incidence of TD. This situation suggests sequestering agent, causes leg defects very sim- a large maternal component, and therefore, female ilar to those seen in classical manganese deficiency, lines would greatly influence the expression. and in fact, successful Mn treatment has been recorded in these situations. Hydralazine blocks SECTION 5.7 Metabolic disorders

CHAPTER 5 281 FEEDING PROGRAMS FOR BROILER CHICKENS d) Spiking mortality lar has been directly related to the severity of the syndrome when it occurs. Calf-milk replacer in Spiking mortality affects young broiler chicks the drinking water is suggested for treatment. This between the ages of 7 and 21 days, and is char- product is high in casein which itself is a rich source acterized by severe hypoglycemia. All affected of the amino acid serine. Blood glucose levels birds exhibit extremely low blood glucose lev- in birds are influenced by glucagon more so than els, which account for many of the observed signs by insulin, and serine is a precursor of glucagon of spiking mortality, including huddling and synthesis. It is possible that ‘all-vegetable’ diets trembling, blindness, loud chirping, litter eating, are ‘deficient’ in serine, and that this predisposes ataxia and rickets. Mortality rates of around 1% the bird to hypoglycemia. In a recent study, we are observed daily for three to five days. Chicks observed reduced blood glucose in broilers fed that survive, experience long-term stunting and vegetable diets, and that this could be correct- growth reduction. There are now field observations ed with milk powder, casein or serine (Table 5.48). of an increasing occurrence of spiking mortal- ity in broilers fed ‘all vegetable diets’. Among Table 5.48 Blood glucose level in 18 many suspected etiological agents of spiking mor- d broilers fed various supplements tality are viral infections, mycotoxins and feed to all vegetable diets anti-nutrients together with poor management practices, although mycotoxins and anti-nutri- Diet Glucose ents have been dismissed as primary causative (mg/dl) agents. The short time frame and low mortali- Corn-soy-meat ty rate experienced with spiking mortality might All vegetable 270ab well be the result of a hormonal or metabolic dis- All vegetable + serine 243b order affecting young chicks during the period All vegetable + casein 275a of rapid growth. All vegetable + milk powder 273a 275a Field reports suggest that diets containing ‘all- vegetable’ feed ingredients produce a much Adapted from A. Leeson et al.(2002 unpublished observations) higher incidence of spiking mortality. The linole- ic acid concentration of these diets in particu- 5.8 Carcass composition obviously, this component has increased as a proportion of the carcass. At comparable weights, D uring processing, cut-up and debon- male and female birds have similar yields of car- ing, knowledge of expected yield is cass portions, and often the female will yield important in efficient scheduling of pro- the most breast meat. However, since the female duction. Carcass composition is affected by live broiler tends to deposit more fat beyond about 2 bird weight, sex of bird and to some extent the nutri- kg liveweight, the yield of edible meat may be less ent content of the diets used and the feeding than for the male if both are fed the same diet. program. Modern strains of broiler have been devel- oped for increased breast meat yield, and so SECTION 5.8 Carcass composition

282 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Energy and crude protein are the nutrients that nent in the carcass changes simply because have the greatest influence on carcass compo- there has been a corresponding change in the level sition. Diets high in energy produce a fatter car- of another component. In fact, the grams of pro- cass while high protein diets result in a leaner tein or meat on a carcass are little influenced by bird. The situation is a little more complex nutrition. Assuming there is no amino acid defi- than this, since it is actually the balance of pro- ciency, then actual protein (meat) yield is dictated tein to energy that is important. If the bird con- by genetics. Feeding more protein or more sumes excess energy in relation to protein, a fat- lysine for example than is required for opti- ter bird develops, whereas a leaner bird can be mum growth is going to have very minimal produced by feeding larger quantities of protein effect on protein deposition. So-called ‘leaner’ in relation to energy. Unfortunately, simple carcasses are therefore a consequence of there changes such as these are not economical, being less fat deposited. The fat content of a car- since the required degree of leanness in the cass is greatly influenced by nutrition. The carcass often only results from uneconomical- more energy consumed by the bird, the greater ly high levels of protein. the potential for fat deposition. Over the normal range of diet energy and protein levels used in When discussing the effect of diet protein or industry, proportions of fat and protein can vary energy level on carcass composition, it is very by about 3 – 4% due to nutrient intake. A 3% important to appreciate the units of measurement. increase in carcass fat will be associated with 3% Often there is discussion about the effects of diet decrease in carcass protein, and vice-versa. on percentage changes in composition, and in Figure 5.8 details the component yield expect- some situations the percentage of a compo- ed from a 2.5 kg live weight broiler. Figure 5.8 Carcass components SECTION 5.8 Carcass composition

CHAPTER 5 283 FEEDING PROGRAMS FOR BROILER CHICKENS The proportional yields are essentially a ical composition of the carcass will also change factor of body weight, and so there will be over time; with increase in the proportion of fat slight changes in major components for lighter and decrease in proportion of protein over time or heavier birds (Tables 5.49, 5.50). The chem- (Figure 5.9). Figure 5.9 Chemical composition of the eviscerated carcass of male broilers Table 5.49 Carcass weight and portions from male broilers (% carcass weight) Live wt. Carcass Abdominal Wings Drums Thighs Bone-in De-boned (g) wt. (g) fat pad breast breast 10.2 14.8 17.6 1224 818 2.5 10.4 13.3 17.0 29.4 18.5 1754 1237 2.6 9.7 13.1 16.5 30.1 19.8 2223 1596 3.0 9.6 13.6 16.3 31.2 20.1 2666 1982 3.3 9.4 13.5 16.0 31.4 20.5 3274 2500 3.5 9.3 16.1 16.0 32.5 21.6 3674 2731 4.2 36.0 23.6 Table 5.50 Carcass weight and portions from female broilers (% carcass weight) Live wt. Carcass Abdominal Wings Drums Thighs Bone-in De-boned (g) wt. (g) fat pad breast breast 10.8 14.4 17.5 1088 720 2.8 10.5 13.8 16.6 29.5 20.4 1582 1160 3.2 10.2 13.6 16.5 29.7 19.5 1910 1376 3.4 13.2 16.4 31.5 21.5 2382 1753 4.3 9.8 13.0 16.4 32.5 21.7 2730 1996 4.3 9.6 34.2 22.6 SECTION 5.8 Carcass composition

284 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.51 Effect of feeding tallow, sunflower oil and flax oil from 28 – 48 d on fatty acid content of female broilers (% of total fat) Body fat 10% Tallow 10% Sunflower oil 10% Flax oil C14:0 2.48 0.28 0.31 C16:0 23.10 10.70 10.9 C18:0 8.28 4.12 4.52 C18:1 41.74 19.09 18.97 C18:2 13.60 61.90 17.8 C18:3n3 1.39 0.99 43.0 Adapted from Crespo and Esteve-Garcia (2002) There is increasing interest in the manipulation the entire grow-out period, since significant of carcass fat composition related to human enhancement occurs from feeding just from 42 nutrition. As with eggs, the fatty acid profile of – 49 d. The data shown in Table 5.52 relate to the diet has a direct influence on the fatty acid the intact eviscerated carcass. It seems as content of the carcass (Table 5.51). though the individual fatty acids accumulate at different rates in different regions of the carcass, The level of supplemental fat used in this study and so marketing strategy may have to be mod- was higher than for commercial application, ified if portions or deboned meat are produced yet there is an obvious correlation between sat- from these carcasses (Table 5.53). uration of dietary fat and that deposited in the body. In terms of producing niche products for Thigh meat yields more omega-3 fatty acids health conscious consumers, accumulation of total than does a comparable quantity of breast meat, omega 3 fatty acids, and that of component which is a factor of the amount of intramuscu- linolenic acid, EPA and DHA are of interest. These lar fat in these portions. However, the greatest long chain omega-3 unsaturates are most eco- effect on fatty acid profile of individual portions, nomically included in the feed as flax and fish is presence or not of skin (Table 5.53). oils (Table 5.52). Unlike the situation with eggs, production of Adding flax to the diet results in enrich- ‘designer’ broiler meats enriched in various ment of linolenic acid, while fish oil results in fatty acids can be complicated by problems of accumulation of EPA and DHA that also contribute off-flavor. With only 0.75% of fish oil in the diet, to the omega-3’s. The accumulation of specif- panelist are reported to be able to detect more ic fatty acids in the carcass seems to be a factor ‘off-flavors’ and rank these meats accordingly. The of dietary oil level and also feeding time. In this marketing of omega-3 broiler meat will require study, the supplements were fed only for the last some entrepreneurial skill in overcoming these 7 or 14 d of growth. It is obviously not essen- challenges. tial to feed products such as flax or fish oil for SECTION 5.8 Carcass composition

CHAPTER 5 285 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.52 Effect of feeding flaxseed or fish oil for the last 7 or last 14 d on carcass fat composition in 49 d male broilers Flax Fish oil Time Linolenic Fatty acid (% of fat) (%) (%) (d) EPA DHA Total omega-3 1.3 - - 7 3.4 00 1.3 10 14 5.3 10 0.75 7 1.3 0 0.1 3.6 - 0.75 14 1.3 - 0.75 7 3.3 0.1 0.1 5.7 10 0.75 14 6.0 10 1.5 7 1.4 0.2 0.1 1.8 - 1.5 14 1.4 - 1.5 7 3.6 0.4 0.3 2.1 10 1.5 14 5.9 10 0.3 0.2 3.9 0.5 0.3 7.1 0.4 0.3 2.2 0.8 0.5 2.9 0.4 0.3 4.5 0.8 0.5 7.7 Adapted from Gonzalez and Leeson (2000) Table 5.53 Total omega-3 content of breast and thigh meat in birds fed flax or fish oil (mg/100g cooked meat) Flax Fish oil Time (d) Meat & Skin Meat % % 14 Breast Thigh Breast Thigh 10 - 14 - 0.75 7 673 995 143 206 10 0.75 14 10 0.75 380 393 182 98 484 708 118 163 858 1309 188 312 Adapted from Gonzalez and Leeson (2002) 5.9 Skin integrity and feather abnormalities a) Feather development F eathers are continuously being shed and feathers in adjacent areas grow, and overlap to regenerated by the bird, and even during cover the entire body. The younger the bird, the the juvenile growth of the broiler, it under- greater the area of apparently featherless skin. As goes 2 – 3 molts. Feathers arise from feather fol- the feathers grow, they conform to the shape of licles that are arranged in distinct tracts on the skin. the bird’s body and may lock together. Abnormal The follicle number is determined by about 14 d feather growth is often noticed when feathers are of incubation. The fact that the body is not uni- not contoured close to the body, and birds appear formly covered by follicles means that certain areas ‘rough’ or with ‘helicopter wing’ etc. Table 5.54 of the skin would naturally be featherless. These shows the composition of feathers from market areas will only receive a protective covering as weight broilers. SECTION 5.9 Skin integrity and feather abnormalities

286 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.54 Composition of feathers Figure 5.10 shows feather yield of sexed from 45 d broilers broilers, while Figure 5.11 indicates standards for length of primaries and back feathers. Crude protein % Total amino acids Feathers are composed mainly of keratin 90 protein that is formed in the epidermis of the fol- Methionine 60 licle. Virtually all growth occurs in the follicle, Cystine 0.7 and so abnormalities seen 2 – 5 cm from the fol- Arginine 5.5 licle will have occurred days or even weeks Lysine 7.1 previously. The keratin structure is very rich in Threonine 2.4 cystine, with each molecule containing around Valine 4.2 8 half-cystine residues, and this is why methio- 6.5 nine/TSAA levels are important for good feath- Magnesium 0.2 er structure. Marginal levels of methionine + cys- Sodium 0.8 tine will cause abnormal feather growth and/or Iron 0.06 reduced feathering, although deficiencies of Copper 12 ppm other amino acids will also cause feathering Zinc 10 ppm problems. With general amino acid inadequa- Selenium 0.7 ppm cy, the primary feathers have a characteristic spoon- like appearance that is caused by retention of an Figure 5.10 Feather yield of sexed broilers. abnormally long sheath that covers the first 50% of the feather shaft. Deficiencies of many Figure 5.11 Growth of wing and back essential amino acids also cause abnormal curl- feathers in male and female broilers. ing of feathers away from the body. Interestingly, these same characteristics are seen with deficiencies Adapted from McDougald and Keshavavz (1984) of some of the B vitamins. SECTION 5.9 Birds fed T-2 toxin (4 ppm) develop only sparse Skin integrity and feather abnormalities feathering, and the feathers that do develop, tend to protrude from the bird at odd angles, leading to some areas of the skin begin exposed. With T-2 toxin, most feathers are affected, unlike the situation with nutrient deficiencies that most char- acteristically first affect the primary feathers. Feather growth is also affected by thyroid func- tion, and thyroid antagonists will delay normal feather growth. Poor feathering is sometimes seen at farms changing from corn to milo-based diets. While a number of diet situations may be involved in such a change, it is interesting to note that milo is very low in iodine content compared to other cereals.

CHAPTER 5 287 FEEDING PROGRAMS FOR BROILER CHICKENS Unfortunately, in most field cases of poor feath- results in less skin collagen production. However, ering, there is no apparent dietary deficiency as gross deficiencies of these nutrients also cause determined by routine analyses or consideration poor growth rate, a characteristic that is not of formulation consistency/changes. Often usually seen in situations of excessive skin tear- problems are isolated to particular flocks with- ing. Unfortunately, there seems to be little ben- in a site where all flocks receive the same feed. efit to increasing the dietary levels of these These factors support the concept of poor feath- nutrients, or even increasing the level of proline ering being caused by infectious agents (likely in the diet. in the feather follicle itself) or factor(s) causing general malabsorption of nutrients. Because feath- A specific dietary situation involves the ers are very fast growing, especially in the first anticoccidial, halofuginone. When this product 7 – 14 d of age their development is very sensitive is fed at normal recommended levels, there is sig- to general availability of circulating nutrients. nificant loss in skin thickness and skin strength, especially in female birds. In one study, using b) Skin tearing halofuginone (at 3 ppm of the diet) resulted in a 50% reduction in skin collagen content and About 5% of downgrades at processing are 50% increase in the incidence of skin tears. due to skin tears. Most tears occur post-mortem, Halofuginone seems to affect skin strength in female and so are related to scald water temperature and birds, more than it does with males, and because pick time. High temperatures with shorter pick the female has an inherently weaker skin, this leads times cause less tears than lower scald tem- to the greater incidence of tearing. It has been perature with prolonged pick time. However, shown that halofuginone interferes with the regardless of processing conditions, a proportion conversion of proline to hydroxyproline in the of carcasses have torn skin. Skin strength is greater skin cells, and that this adverse effect cannot be in males vs. females, and for both sexes, it corrected by adding more proline to the diet. increases with age. Most problems are therefore encountered with carcasses from younger female When skin tearing is a problem, assuming that birds. There is a genetic component, because dif- processing conditions have been scrutinized, the ferent strains show differences in skin tearing, and only potential nutritional factors involved are in one study it was shown that skin from slow feath- halofuginone and level of zinc, copper and ering strains was less elastic than that from fast vitamin C. Skin tearing is more problematic in feathering birds. hot weather. This situation leads to recom- mendations of supplemental vitamin C, although Skin strength is highly correlated with its col- birds under these conditions almost always lagen content, and so skin with greater collagen carry more subcutaneous fat. Feeding higher lev- content is less prone to tearing. Any nutrition- els of crude protein has also been shown to al factor that influences skin collagen content will increase skin strength although the reason for this therefore indirectly affect susceptibility to tear- is not clear. More crude protein may provide more ing. The amino acid proline is a component of of the non-essential amino acid glycine which hydroxyproline which itself is responsible for the accounts for about 30% of the amino acids in col- stability and rigidity of collagen. Zinc, copper lagen, or alternatively more protein per se may and vitamin C all play a role in collagen synthesis simply reduce carcass fatness. and so deficiencies of any one of these nutrients SECTION 5.9 Skin integrity and feather abnormalities

288 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS c) Oily bird syndrome (OBS) sibly due to there being less subcutaneous fat. Males also exhibit more insoluble skin collagen, As its name implies, birds with OBS have skin and so this may be important in reducing prob- that is oily or greasy to the touch. OBS is lems of solubilization and water uptake as often observed most frequently in older broilers and occurs with OBS carcasses in chill water tanks. especially those fed high-energy diets in the warmer summer months. The problem also The main collagen layer in birds with OBS seems to relate to specific processing plants, where is 30% weaker at normal body temperature the occurrence is greater with the increased and up to 50% weaker at temperatures used dur- ‘stress’ applied during processing, and espe- ing processing. The problem may relate to cially plucking. Interestingly, the condition is rarely impaired collagen crosslinking. In mammals, and seen in hand-plucked birds. The condition is also in the formation of eggshell membranes, lysyl oxi- associated with increased water retention in dase is thought to be the only enzyme involved the carcass, especially in regions of the car- in crosslink maturation of collagen and elastin, cass where skin ‘elasticity’ had been affected. These converting lysine and hydroxylysine into alde- pockets of water are most often seen in female hydes. Lysyl oxidase is a copper metalloenzyme birds. The problem is most noticeable in pock- that requires pyridoxal phosphate as a co-factor, ets of the skin that separate in the back region. and copper deficiency is known to impair nor- Because the skin seems more prone to tearing, mal collagen crosslink structure. However, it does these pockets rupture and the surrounding skin not seem as though copper deficiency is the sim- becomes noticeable oily. ple solution to this problem. A general finding in situations of OBS is a OBS occurs only in broilers grown in warm cli- change in the skin ultrastructure, such that mates, and experimentally the syndrome can either the layers of skin separate to allow the pock- only be duplicated by using warm growing con- ets of oil and/or chilled water to accumulate, or ditions. At higher temperatures, birds carry more the skin tears more easily. Apparently, fat satu- subcutaneous carcass fat, and so this may be the ration is not a factor in OBS, rather there is trigger mechanism. Because of the oily nature of some change in the integrity of the various lay- the carcass, various diet ingredients and nutrient ers of the skin because the skin from affected car- levels have come under investigation. Fat levels casses is easily separated and removed from the and sources in the diet have come under close scruti- underlying musculature. The five collagenous ny, although there does not seem to be a simple layers beneath the epidermis seem less compact relationship. Higher levels of fat and/or energy in than normal, and the deepest layers contain relation to the level of protein in the diet have caused the most fat cells. more problems, although research results are inconsistent. Even though the bird’s skin has an While there is no real change in total skin thick- oily appearance, levels of unsaturated fatty acids ness with OBS, its breaking strength seems to be do not correlate with OBS, and in fact, more reduced. Although males usually have thinner problems are seen in birds fed tallow. skin than do females, it is usually stronger pos- SECTION 5.9 Skin integrity and feather abnormalities

CHAPTER 5 289 FEEDING PROGRAMS FOR BROILER CHICKENS If OBS occurs, then the only immediate environment are of questionable value. While practical solution is to modify the processing con- fat levels in the diet do not seem to be a factor, ditions, and in particular, scald temperature there is an indication of more problems occur- and pick time. Because the exact cause of ring with saturated fats such as tallow. The diet impaired collagen crosslinking has not been should contain adequate levels of copper and not identified, then other changes to the diet and/or contain excessive levels of zinc or vitamin A. 5.10 Environmental nutrient management M anure composition is now a factor in as zinc and copper and this is leading to re-eval- diet formulation. With the concen- uation of dietary needs for these trace minerals. tration of broiler production in many world locations, disposal of manure is now a con- Broiler litter is relatively bulky and of low nutri- straint to production. The actual concern today ent concentration compared to cage layer manure. is disposal of manure in a manner commensu- The litter composition is dictated by the amount rate with environmental regulations. Most broil- added to the broiler facility prior to brooding, and er farms are situated on a minimal land base and since there is little change in this quantity over so, meeting environmental regulations now time, this amount is predictable at time of clean- means transporting manure some distance from out. The most common litter materials used the farm. Where such transportation costs are today are wood shavings, straw and rice hulls. All prohibitive, then incineration is an option. of these litter materials contain negligible quan- tities of nitrogen and phosphorus. The current major concern with litter disposal, is its content of nitrogen and phosphorus. There Table 5.55 outlines a series of calculations is also awareness of content of other minerals such based on 10,000 broiler chickens eating 45,000 kg of feed. SECTION 5.10 Nutrient management

290 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.55 Calculations of manure production and composition per 10,000 broilers Dry litter material 2,000 kg Feed intake 45,000 kg @ 90% DM @ 70% metabolizability 12,000 kg dry matter excreted @ 60% DM 20,000 kg ‘as is’ excreta 22,000 kg ‘as is’ litter Wood shavings/straw/rice hulls = 17% of DM of litter Excreta = 83% of DM of litter Wood shavings, etc. = 6% of ‘as is’ litter Excreta = 94% of ‘as is’ litter Litter = 4% N, 3% P2O5, 2% K2O on ‘as is’ basis 20,000 kg @ 4% N = 800 kg N @ 3% P2O5 = 600 kg P2O5 @ 2% K2O = 400 kg K2O Feed intake and metabolizability of feed are is at high humidity, and close to saturation at a going to be fairly consistent across the broiler indus- high temperature, there will be minimal moisture try for a given weight of bird. Consequently, the pick-up. If birds have loose and sticky manure, dry matter excretion of the flock will be quite pre- as occurs with some disease challenges or feed dictable. The major variable will be the dry passage, the water holding capacity of excreta matter content of the final litter, and this will direct- increases, and regardless of ventilation rate and ly influence ‘as is’ concentration of nutrients. The humidity, the excreta releases little moisture, moisture content of litter will be a factor of and again, this contributes to wetter litter. Diet water intake, water holding capacity of the exc- formulation will also influence water intake, reta, ventilation rate and humidity of outside and so litter moisture content. High levels of pro- air. In the example shown in Table 5.55, a value tein, sodium and potassium are most often the rea- of 60% DM was used in the calculation. This sons for increased water intake. means the litter has a water content of 40%. The above variables can combine to produce litter at The nitrogen and phosphorus content of 25-55% moisture in extreme conditions. broiler feed has a direct effect on the content of these nutrients in manure. There is little varia- One of the main reasons for ventilation is to tion in nitrogen content of broiler diets fed remove moisture from the building. If outside air worldwide, and relatively little scope for further SECTION 5.10 Nutrient management

CHAPTER 5 291 FEEDING PROGRAMS FOR BROILER CHICKENS reduction. Each 1% reduction in dietary crude pro- There are obviously lower limits to phos- tein influences litter nitrogen by only about 0.2%. phorus content of diets, and the requirement for Considering the size of the broiler industry today, skeletal integrity is often higher than needs for gen- a 0.2% reduction in manure nitrogen content is of eral performance. The lower limits to diet phos- global significance, yet at the farm level, this phorus levels are therefore often dictated by car- change is of little economic importance. As the pro- cass processing conditions. There is little doubt tein content of diets is reduced, there is often loss that diet phosphorus needs decline over time in broiler performance, even though levels of and that very heavy broilers have minimal require- methionine + cystine, lysine, tryptophan and even ments. For broilers much older than 60 d, it threonine are maintained by use of synthetic seems as though conventional ingredients, even amino acids. Because protein and amino acids are of plant origin, can provide adequate phospho- relatively well digested by broilers, then there is min- rus for 10 – 14 d. imal scope for reducing litter nitrogen content by diet formulation. There is more scope for reduc- When calculating manure phosphorus appli- ing the phosphorus content of broiler litter through cation rates, and the potential for run-off into simple reduction in total phosphorus content of the streams etc, the situation is clouded by the con- diet. Depending on bird age only 30 – 60% of diet cept of soluble vs. insoluble P in manure. The phosphorus is digested, and so the vast majority of use of phytase does not seem to increase the pro- ingested phosphorus is excreted in the manure. There portion of soluble phosphorus in manure. is also more variance in diet phosphorus than for Soluble phosphorus will presumably be available diet nitrogen, so again there is greater potential for to plants, while truly insoluble phosphorus will standardization. The situation with phosphorus is be unavailable. Manure phosphorus that is also helped by the availability of phytase enzymes. soluble in citric acid is often considered as a meas- Most phytase enzymes will liberate the equivalent ure of the phosphorus available to plants. If of 0.1% available phosphorus and so diet formu- phosphorus is soluble there is concern that lation can be adjusted accordingly. There is a more will be lost as run-off into streams. direct relationship between dietary available phos- However, the alternate argument is that truly insol- phorus and excreta phosphorus (Figure 5.12). uble phosphorus will not leach into soil, and so will always be subject to physical run-off depend- Figure 5.12 Manure Phosphorus output per ing on topography of the land. This issue seems 20,000 2.5 kg broilers to be a factor of soil chemistry, topography, season of manure application to land, and level and intensity of rainfall. With all of these vari- ables, it is obvious that unanimous conclusions about the importance of phosphorus solubility in manure are not likely in the near term. Of increasing concern is the level of trace min- erals in broiler litter, again as it influences soil accumulation and water leaching. In some regions of the southern U.S.A. it is no longer pos- sible to use broiler litter as fertilizer on land used to grow cotton since the accumulated zinc con- SECTION 5.10 Nutrient management

292 CHAPTER 5 FEEDING PROGRAMS FOR BROILER CHICKENS tent of soil greatly reduces plant growth. Of poten- ably there is greater bioavailability of minerals tial concern is the accumulation of zinc and cop- such as zinc from corn and soybean meal. per in soil. Table 5.56 describes average min- There may be up to a 10% increased bioavail- eral content of poultry litter. ability of zinc as a result of using phytase. It seems as though it is theoretically possible to greatly The zinc and copper levels in manure are reduce trace mineral supplements in broiler directly related to diet inclusion levels. Mineral diets, thereby reducing their accumulation in premixes usually contain around 80 ppm zinc manure. and 10 ppm copper. The bioavailability of trace minerals in the major feed ingredients is large- Trace mineral proteinates, although much more ly unknown, and in most situations their con- expensive than oxides or sulfates, are of more pre- tribution is ignored. The major ingredients do dictable bioavailability. In using very low lev- however, contain significant quantities of most els of trace minerals under experimental conditions, trace minerals (Table 5.57). we have recently used such mineral proteinates because of their high and consistent bioavailability. If copper was 100% bioavailable in corn and In this study, birds were fed a conventional soybean meal, then there would be little advan- mineral premix using oxides and sulfates. The tage to using supplements. The limited data avail- supplements were arbitrarily assigned a digestibil- able on trace mineral availability from work ity value of 70%, and then this level of ‘digestible 20 – 40 years old, indicates values of 40 - 70%. minerals’ provided as mineral proteinates. The use of phytase further complicates the issue, Mineral levels were further reduced by using only since some of the minerals present in natural ingre- 80% 20% of these already reduced con- dients (Table 5.57) will be present within the phy- centrations (Table 5.58). tate molecule. When phytase is used, presum- Table 5.56 Trace mineral content of broiler litter Dry matter Mineral (ppm) As is (40% DM) Zn Cu Fe Mn Mg Al Ca Na 300 500 3000 400 6000 2000 3000 4000 120 200 1200 160 2400 800 1200 1600 Table 5.57 Trace mineral content of selected feed ingredients (ppm) Corn Zinc Manganese Iron Copper Soybean meal Meat meal 12 10 107 11 Wheat shorts 37 19 184 15 97 7 285 12 76 104 203 16 SECTION 5.10 Nutrient management

CHAPTER 5 293 FEEDING PROGRAMS FOR BROILER CHICKENS Table 5.58 Broiler performance and calculated mineral output in manure from a farm growing 5 crops of 100,000 male broilers annually Treatment 0-42 d F:G Mineral output (kg/yr) Wt gain (g) Zn Mn Fe Cu Inorganics1 1.75 Bioplex2 2217 1.70 470 273 535 19 Bioplex 80% 2351 1.73 318 217 523 17 Bioplex 60% 2239 1.72 294 185 491 18 Bioplex 40% 2285 1.74 309 172 494 16 Bioplex 20% 2185 1.69 299 156 487 16 2291 292 130 446 15 1 Zn, 100 ppm; Mn, 90 ppm; Fe, 30 ppm; Cu, 5 ppm 2 Zn, 70 ppm; Mn, 63 ppm; Fe, 18 ppm; Cu, 3 ppm Using the 20% inclusion of the mineral reduction in copper output in manure. If there proteinate, supplements were Zn, 14 ppm; Mn, is future legislation concerning trace mineral con- 13 ppm; Fe, 3.6 ppm and Cu, 0.6 ppm. Even at tent of manure, much as now exists for N and these low levels, broiler performance was unaf- P in many countries, then it should be possible fected. Based on a 3 d total collection period to reduce levels by nutritional intervention. If of manure at 18 d and at 39 d, it was possible such legislation occurs, it will be interesting to to predict manure mineral output extrapolated see what happens to the current common prac- for the 42 d grow-out period (Table 5.58). There tice of using high levels of copper as an anti- was a 37% reduction in zinc output and 21% bacterial agent. SECTION 5.10 Nutrient management